GRID is great fun!
After playing the free GRID Dmmo (v1.0 released in April/May 2008), I bought GRID the first day it hit local retail store on 6/4/08 (I didn't want to wait for shippimg delay, sorry Amazon), and have been playing it non-stop ever since. I've completed the offline GridWorld career against the excellent in-game AI drivers, and now mostly play online multiplayer. I occasionally re-run some career events and frequently practice in RaceDay against AI because they are so fun. On & offline, GRID runs great (typ 80-100 fps) on my above-spec desktop PC (Core2Duo 3Ghz, 8800GT/512MB video card, G25 wheel+pedals), check your system against the specs to be sure it'll run well on your PC. As others recommended if you're unsure if your PC can handle it (or you want to check out the game's look & feel), download and play the FREE v1.1 Demo. If you do buy GRID PC DVD, be sure to download and install the v1.2 patch - it has some fixes and adds some nifty options (including optional Assists Disabled and optional Collisions On/ Forward Only/ Off settings for hosting online racing). I've read in CodeMasters' Grid forum that Console (XBox, PS3) patch to date lacks some of the v1.2 PC patch features.
Handling with wheel is exceptional, but undriveable (at least for me & most other players) with keyboard. Handling varies for various gamepads (probably related to whether pad has analog or digital outputs), I suggest you read the forums if you're a gamepadder (I'm not).
CodeMasters recently announced they will release a download content (DLC) package this Fall - no details currently on full content (additional tracks,if any, unknown; at least 2 additional cars ahve been announced, the McLaren F1 sports GT and the Nardo VW W12 GT), and currently unknown if this forthcoming DLC will be free or not (I'll pay whateber they charge!).
GRID is more toward arcade behaviour than their earlier ToCA Race Driver 2 (get it!), and much more arcade style than simulation race games including SimBin's GTR2 and Race07 WTCC. Hence GRID is easier for the non-hardcore gamer than the steep learning curve fullon cutomizable simulation games. If you're hardcore sim, you probably won't like GRID's lack of car tuning (personally I enjoy GRID's level playing field, and it's awesome + easy paint jobs). If you're not hardcore simmer, I think you'll find HRID is really fun, Terrific graphics (btw there are some config tweaks posted in forums to reduce blur & HDR and to improve color saturation much to my liking); very good audio, great AI, 3 Assist parameters each optionally On/Off, smooth netplay, etc., etc. Get GRID!

Great Racing Game!
This game was really frustrating with a keyboard but once I got a PS2 style controller I couldn't stop playing. It's a great game and the drift gp matches never get old!!!

GRID
I have never been much of a computer gamer, but since getting a late model computer with a high end graphics card, I have tried several driving games and this is my favorite. Good blend of realism and arcade. Don't bother unless you have a good steering wheel with feedback. I spend more time than I should playing it.

Wow!
Best eye candy of any racing game out there. If you have a fast PC and are fans of either racing games or racing sims, buy this immediately. Races are categorized as American Muscle, European and Japanese. The damage model looks good and works well. The demolition derby races are AWESOME.

Excellent racing, nice mix of arcade and true racing
Excellent gameplay, stunning graphics, runs even smoother than its predecessor DiRT. Do install the version 1.2 update, at least for me otherwise the force feedback of my Logitech Driving Force steering wheel did not work (didn't work in the downloadable demo either). Also tweak the sensibility settings of the steering wheel as otherwise the game is way too difficult. Once that's done it plays like no other, good balance between arcade and real racing. A true adrenaline booster!