I got some quick impressions on games people have been asking about.
A.D.D. - This game can't hold a candle to Warioware: Twisted, which is a shame since the hardware to pull it off is all there. Not only are the games not nearly as polished, with many too confusing or too simple, but the transition between microgames has a weird hitch on my 3G that totally breaks the pacing. It's not a long hitch, mind you, but it annoys me. The fact that your trying to figure out what to do in 3 seconds or less with your fingers obscuring all the your visual cues doesn't help either. It's not a terrible game, but not a good Warioware replacement IMO.
Blades of Fury - This is a silly button masher that looks similar to Soul Edge and the like. There's not much strategy here, and the story is ridiculous, but it looks good and isn't terrible. If you just wanna mash some opponents without any real combos or ability it's not bad at all. Local multiplayer is finicky (example: a 20% battery warning will nuke the connection between devices) but works well enough for a few quick matches.
Earthworm Jim - Graphically this looks great and it runs pretty well on my 3G. The controls are a little iffy, mostly in regards to jumping. It's hard to time the jumps on the tires on the first level, for example, to get the extra height you get from jumping instead of just bouncing up and down. Luckily, the difficulty modes help make up for the controls.
Ravensword - I've been having some trouble with the controls on this game. Using my right thumb to swipe on the screen and adjust the view only seems to register about 60% of the time, which makes it a bit of a pain to play. Hopefully they can improve this because it seems pretty cool aside from that glaring flaw. I haven't heard of many other people complaining about this though.
Skater Nation - From what I played on a friends 3GS today, it's not so hot. You use one button for jumping, flip tricks and grinding IIRC, and the other button for grabs. More buttons would be preferable, but whatever. Grinding may have been on the grab button, but anyways, it's weird to keep tapping the same button to do things. The main problem is the analog stick sucks, and it's hard to turn. Gameloft seems to have more problems with virtual analog controls than any other big publisher on the platform, unfortunately.
Jet Car Stunts - This game is awesome. The controls are spot on, the graphics are really good and it runs great even on a 3G. The look kinda reminds me of Mirror's Edge. The tracks are pretty well designed and it's real fun to compete with a buddy over OpenFeint with high scores and stuff. Definitely one of my favorite games on the iPhone.
Asphalt 5 - This game isn't bad, but it's not excellent either. That said, it's probably the best arcade racer in the store (maybe excluding the dated but still awesome Fast Lane). It runs decently on a 3G, but the animations for powersliding and ramming into other cars look pretty bad, like they were lifted out of Cruisin' USA or something. Still, not a bad choice for what it is.
Doom - A well made port, but I dislike how all the levels from single player are unlocked and ready to jump into from the get go. This has kept me from playing it much, because I don't feel like I'm progressing and I've already beaten the game countless times. The local multiplayer isn't bad though, although many of the maps are horribly balanced since they weren't really designed for multiplayer all those years ago (although that didn't stop people back then).
Rock Band - My favorite music game on the platform. It only has 20 songs, but you can buy more for 50 cents each. The multiplayer here is pretty cool, I only tried the local but you can get up to 4 players. I was bummed that the vocals don't actually have you sing like in the console versions, considering there is a microphone built into the device. You just push buttons along with the lyrics. This plays way better than the Tap Tap games IMO.