As usual, I’m way behind in trying out the new fall shows and am running out of room on my DVR. The shows I have recorded but not watched yet are:
Grimm
Terra Nova
American Horror Story
Once Upon a Time
For what it’s worth, I’m enjoying Revenge, Ringer, and Person of Interest.
I’ve been burned in the past (The Event, FlashForward, V) and hate to get involved in a show that either gets bogged down quickly or canceled too soon.
I’m still hanging with Terra Nova, but, to be honest, it’s pretty dumb. Mostly, I’m enjoying it because it is something my teenaged son and I watch together.
I gave up on Terra Nova after the pilot. For a show about time travelers and dinosaurs, it didn’t grab me as much as I felt it should have. I thought there was too much time spent on the kids, and the stuff with the kids felt very soap-opera-ish. I don’t know if it’s gotten any better.
I thought the pilot of Grimm was interesting, but I stopped recording it because my DVR can only record two shows at once, and I was already devoted to both Fringe and Supernatural.
I like American Horror Story a lot, but it’s an acquired taste. The show is bananas. It’s not everybody’s cup of tea. You might want to give the pilot a try. If the pilot doesn’t grab you, feel free to delete the rest of the run.
I’m also liking Once Upon a Time – but it’s good, not great. I can’t put my finger on what it is missing that would make it truly great (other than just better acting and writing), but the concept has captured my interest to make me keep coming back. I’ll stick with it awhile. It will probably be cancelled soon enough anyway.
In general, I’d say you should watch the pilot of each one you’ve listed (or maybe half the pilot, if you’re pressed for time) and go from there.
No one mentioned the actual correct solution - upgrade the drive space in your DVR! (If possible, of course.)
I’ve taken to recording lots of shows that I don’t watch immediately, and save whole seasons for those lazy days of summer, or whenever you want to veg out. I think that Revenge and Ringer are not going to get watched any time soon…
That being said, I’d also suggest dropping Terra Nova. The pilot was so boring, I didn’t even finish watching it.
I struggled through 3 episodes of Terra Nova and gave up on it.
I haven’t given up on Terra Nova yet, but if you need space on your DVR, you could check Hulu.com and see which shows can be watched there, then delete those from your device (of course, that may only work if you are in the US).
I think Grimm is pretty decent, interesting enough to keep.
I’m LOVING Once Upon a Time…so I greatly recommend watching as much of that as possible
I think it lacks any structure in the episodes. It hasn’t figured out how it’s going to handle its main conceit, or make it last, so they’re stalling. However, I like the characters, so I will keep watching for now.
I’m really liking the American Horror Story so far, but it’s not for everyone. I think the pilot is pretty representative of the show, so you should watch it, and keep watching if you like that episode, or delete the rest if you don’t.
Terra Nova is worthless, stupid trash and it doesn’t even have any decent dinosaurs.
Exactly what I was going to say.
The rest of the OP’s list is (was) sitting on my DVR unwatched, and when I was forced to do a mass purge of around a dozen movies and a show, I chose to delete Terra Nova sight unseen based on not reading a single positive thing about it either online or in print.
Just read last night that Terra Nova’s ratings are bad enough that it would have been cancelled except that postproduction takes so long on eaxh episode that the initial 13 episode run (after which they pick up the full 22 or cancel it) constitutes the entire first season, so no axe needed to fall.
Another vote for American Horror Story- oh boy it’s grim…and weird. But I’m hooked.
My sympathies to the OP. Ever since the wizards at FX killed Terriers I have had no intention of allowing myself to get caught up in a new show. That plus their keeping The Killing on for another year convinces me that I’m a bad judge of TV show quality.
This season we had DVR’ed these shows that we wound up dumping without so much as a twinge of regret:
Unforgettable
Revenge
Body of Proof
Prime Suspect
Person of Interest
I wasn’t remotely interested in Terra Nova to start with. I watched two (actually 1 and 1/2) episodes of American Horror Story before deciding it was not going to be for me.
Our solution came in the form of “if we had more than two episodes in the queue and couldn’t work up the interest to see one of them, we just shitcanned the batch.”
Of course we still have a dozen or so shows we still watch from earlier seasons, so it’s just the new batch that we’re being cavalier about.
YMMV
Grimm is pretty good if you like modern fairy tale redux.
Terra Nova is barely watchable. I haven’t given up on it yet, but only because I’m a sucker.
American Horror Story is not something I even considered watching.
Once Upon A Time is interesting.
If you have to pick one, I’d throw out AHS, because I wouldn’t have recorded it to begin with.
If you have to pick two, Terra Nova should get the axe.
Or you could, you know, have a TV marathon and watch some stuff. 
Do what I did: have the hard drive start to fail and then, even though the portion of the drive your DVRed files were on isn’t affected by the actual failure, somehow manage to corrupt the files in copying them to a new drive.
Unforgettable is reasonably followable. I’m thrown by Poppy Montgomery’s accent, though. She’s supposed to be from upstate New York, but keeps having southern accent slide through. And she’s from Australia, so it’s not her native accent. I was worried the conceit about her personal memory helping her solve crimes would get old - there’s only so many times she could be an actual witness to the crimes before that strains credibility. But they have managed to give her other ways, like remembering touring the crime scene when they later find something out, and being able to remember some detail she observed. Of course they have her picking details out of the background reminiscent of hitting “resolve” on digital camera video - like reading something on an object in the background. And the way they pull off the memory is to have her standing inside the scene watching herself. At least the FX is much better than Ringer. But as long as she keeps wearing tank tops to do her job, I’ll probably keep watching.
Haven’t looked at Revenge.
Body of Proof is okay for a crime procedural. Assuming you let the coroner conduct suspect interviews, etc.
Prime Suspect has been canceled. Too bad.
Person of Interest is still holding my interest.
Does anyone have an opinion on whether I should bother catching up with Homeland? I watched the first 2-3 episodes, but now I’m a month behind: I’m thinking that if I’ve let it get to this point I must not be interested anymore, but I also feel like it had potential.
Regarding the OP:
[ul][li]Grimm - I’m hanging in there, but I don’t like it as much as Once Upon A Time. If something interesting doesn’t happen soon, I’ll probably stop watching it.[/li][li]Terra Nova - Not watching it (had no interest).[/li][li]American Horror Story - I love it, but have gotten a couple of episodes behind. I plan to catch up this weekend.[/li]Once Upon a Time - I’m surprised by how much I like this show.[/ul]
I’m liking the show and have watched some of the episodes on On Demand. That could help you decide.
The main characters are well drawn enough that anything is possible, especially Mandy Patinkin’s. The twists are easy to accept and there’s always the hint that something below the surface isn’t being addressed at the moment but will come up as significant later.
Dump Terra Nova. It will almost certainly be cancelled anyway, so why bother.
I like Homeland. Definitely watchable.
Oops, I forgot to specify that I have all of the episodes on my TiVo (and still have my season pass): I just keep seeing all of those unwatched eps in my To Do list and wondering if I should bother. 
Thanks! Now I’ll probably give it another shot this weekend.