Dirt 1 is getting on a bit now, you are talking a 4 year old game, which is a long time in terms of computers and the progression of graphics, so compared to Dirt 3, which is the one that just came out, it is going to look bad, but at the time it looked amazing.
And the controls are for a pad or wheel because it is a racing game. Although you can play with your arrow keys, racing games are designed for a specific controller rather than mouse and keyboard which most other PC games are.
I've not played it so can't really say what I think of it, but regarding the later ones I agree with Linkin that Dirt 2 had too little rally, and Dirt 3 has too little everything, all of the events are way too short. I want some that are full endurance, lasting a long time over several stages, not events lasting at most 5-10 minutes