I was really surprised to come across Mass Effect and Nights Into Dreams. Any other games I might like? Generally speaking I like RPG’s, older platform games, puzzle games (Like Lemmings, not match 3), and SF and fantasy themed action/adventure games.
Journey. It’s worth every penny, and then maybe a few more.
For Platformers: Mega Man 9. Hands down the best “8-bit” platformer of the last 5 years. Mega Man 10 isn’t as good, but it’s out there.
A lot of the PS1 and some of the PS2 era RPGs are available on PSN. I don’t have a list, but Sony put some effort into getting people to buy their games again.
There’s a LOT of good stuff on PSN, though its strengths actually lie in ports of old PS1/PS2 titles moreso than actually original content (Which is generally better on XBLA, though there’s a lot of overlap.)
In terms of actual “new” games (i.e. games that aren’t ports from older consoles):
BloodRayne: Betrayal is suprisingly good considering where its license comes from. It’s a platform/brawler sort of thing, with more emphasis on the latter than the former.
Castle Crashers is a flat out brawler that is just hilarious and awesome, especially with friends.
Crazy Taxi is technically a port, but not from an old Sony console. Remains one of my favorite games on the Dreamcast, and the PSN port is… good, but lacking the hilarity of the licensed soundtrack, alas.
Dyad is a really interesting sort of… I dunno. Rail shooter-ish type of thing. Indie title, kinda trippy.
From Dust is a modern take on the ‘god game’ genre ala Populus.
Hard Corps: Uprising is basically a modernized Contra, and tons of fun, but hard.
Jet Set Radio is another Dreamcast port, of an excellent, very unique action game.
Journey has already been mentioned.
Lemmings - apparently there’s some version of this on PSN. Haven’t played it, but since you specificially mentioned the title…
Might & Magic: Clash of Heroes is a puzzle game laid on top of a fantasy RPG format, or, maybe, a puzzle game with an FRPG story attached, or something. Anyway, it’s a pretty good puzzle game (admittedly closer to the match 3 variety than to lemmings) and a pretty entertaining story as well.
Pac Man: Championship Edition DX is… Pacman updated for the 21st century. Frenetic, hypnotic and generally addicting. And I say this as someone who didn’t really like Pac man.
Both Penny Arcade Adventures games are pretty entertaining light JRPG style fare.
Plants vs Zombies is… Plants vs. Zombies. EVERYONE likes Plants vs. Zombies.
Retro/Grade is a rhythm game disguising itself as a shooter. You fly backwards through time undoing your own shots. Try the demo.
There’s demos for most but not all of that stuff (Which is kinda stupid since all of it has demos on XBLA) so try before you buy and all that.
I think Okami HD is also out, with Move compatibility if you want to use motion controls for the brush (which, having tried the Wii version, I do not recommend unless it’s vastly improved).
I’ve never played it, but Sound Shapes looks interesting. I was thinking of downloading for my son.