You will know by the time you get to the 6th season of the show whether you like it or not. It found a formula that worked for it (case of the week, with random spoof/homage episodes thrown in and continuing character development) and did not really deviate from it. They got even better being absurdly funny at one moment (such as the vampire episode with the original Buffy Kristy Swanson) to extreme drama (like the cliff hanger of the season finale), and sometimes managed to do it in the same episode. The standout episode of the season were, to me, This Episode Sucks, which was the vampire episode, Heeeere's Lassie, a shining inspired episode with Tim Omundson and Dule Hill in a great chase sequence, and Indiana Shawn and the Temple of Kinda Crappy, Rusty Old Dagger, which is spoofing exactly what you think, and saw the return of Cary Elwes, and guest starred the nearly ageless Mädchen Amick.
If you really like the show, you will realistically like every episode. I definitely think the series benefited from having shorter seasons. Had each season had 22 episode runs all the way through it would have likely got much more stale, but since they kept the number of episodes at 16 or less, I never felt that it got too repetitive. And, they kept coming up with funny and original stories that even when they went back to older characters and continued story lines, they never did the same thing twice.
For those who do get the DVDs, the extras are pretty much the same as in prior seasons. There are definitely not as many audio commentaries for episodes, but each one does have a video commentary with the writers, there are deleted scenes for most of the episodes and a gag reel. All in all a lot of extra material for those who like going through all that stuff. If you have liked the show up to this point, I think you will like this season, and if you like the extras the DVDs are definitely worth adding to your collection.