Garnett played a solid game and his defense was key on Gasol. That said, you can see that KG is not the same player he was 2 years ago. I'm convinced he is still hurting but not letting on that anything is wrong. He seems tentative on offense (but give some credit to some decent LA defense).
What KG has done is re-invent himself as he's gotten older and more hobbled.
There is some truth in the fact that KG isn't back to what he was, but I think that tends to obscure from people what he's actually doing. I made a post before the Finals began, detailing how he hadn't just outplayed good players like Jamison, Lewis and Beasley 1-on-1, he'd terminated them. Just completely outclassed them. Well, quiet as kept, since game 1 of the Finals he has done the same thing to Gasol.
If you look at his per-game averages these Finals, Gasol looks really good (18.8 points, 10.0 boards, 2.6 assists, 52% FG). But if you look just at when he's been defended by Garnett, those numbers look a lot different. When Gasol and Bynum are on the floor together, KG defends Gasol as his primary assignment (when it's Gasol and Odom, KG usually takes Odom). In game 1 Gasol scored 16 points and grabbed 8 boards in the 23 minutes that KG defended him (vs KG's 12 points and 0 boards in that same period).
But in the 4 games since then, by my calculations (via popcornmachine.net and the game logs) Gasol has scored a total of 14 points in more than 70 minutes when KG had him as the primary defender. Break that down to per-36 minute stats for clarity, and in games 2 - 5 when KG defended Gasol they have averaged:
Gasol: 6.8 points, 50% FG, 8.3 Reb, 2.0 ast, 1.5 TOs per 36 min
Garnett: 18.6 points, 65% FG, 8.8 reb, 4.9 ast, 2.0 TOs per 36 min
Again, this is over the last 4 full games when KG has had Gasol as his primary defensive assignment (essentially when they're going head-to-head). I'll be honest, I just ran these numbers and they're so stark and 1-sided that I almost wonder if I made some mistake. But it's all on spreadsheet, and I'm confident that they are pretty close to accurate.
So I'd say don't focus so much on what Garnett was in 2008...I say look at what he is now, and after getting smacked in the mouth in game 1 it looks a lot like KG's been making Gasol his son when they match up. And before the series, there were many making the argument that Gasol is currently the best offensive big man in the NBA. If Gasol is anywhere near the best big man in the NBA, I'll let you do the math on what that would make KG based on these Finals...