It's a boring game when you're way out in front. It's also a frustrating game when you can't do a thing, and you're driving like mad to catch up to the 5th place car. I'd rather have a chance of winning, and catch all the way up on merit. Also, I've had some great racing that wasn't for the lead.
One thing that bothered me was a win at the Pro FF at Deep Forest. I was racing a full-tilt Acura ITR, and was quite fast. However, the tires were crap. I was catching up another car at a rate of about 2 seconds a lap after my stop. I caught the lead Spoon Civic with a quarter of a lap to go. It felt like a hollow victory, making up 4 seconds on the final lap, even though I hadn't set the best time. I feel the AI allows you one final chance to beat it on the last lap sometimes.
The AI's much more screwy at times: Sometimes it's boosted so you can't catch them without kicking the snot out of it with many mods, and at other times, it's as if they were carrying an ton of ballast. I've had some good racing for 2nd, 3rd, or even 4th place, but I can't think of too many battles for the lead worth savoring in GT3. Sometimes the lead AI car is leagues ahead of the other 4 cars, and it's tough to choose soemthing that allows you to "race" the other 4 cars and still be competitive enough to beat the best AI car for the lead.
GT2's AI were lousy drivers, but at least there was an element of predictability that prevented them from cheating and made for other competitive AI cars. The same AI car didn't always come in 2nd in the same race, for example.