We spent much of the weekend obsessing about the original British version of The Office. I know I'm a little late to the party on this but now that we have the DVR, we've been taping both the American and British versions. We had only seen the American version until about 2 weeks ago when I found the British version while searching for stuff to record on the DVR.
The first episode we saw was Series 1, Episode 4, which it appears is generally considered to be the apex of the show. The link has a plot summary and a clip but it features Brent singing "Free Love (on the Free Love Freeway)" which can be found here. One of the funniest things I've ever seen. (That last link is to a fan site that also has a download of the very good version of "Handbags & Gladrags" that's the show's theme song.)
It's tough to watch back-to-back-to-back episodes as we've been doing because people aren't meant to be uncomfortable for that long. We've watched all of Series 1 and are part way through Series 2. Without ruining anything, Series 1 appears to be better. I think it's because Brent becomes less likeable in the second season. The DVD also has some excellent special features and it can help to watch with the subtitles on. Some of the British slang can be hard to catch without them.
As far as comparisons to the American version, I think they're both good with the obvious edge going to the original. My impression is that Ricky Gervais's David Brent doesn't realize he's such an idiot so you can feel sorry for him, but Steve Carel's Michael Scott is much more self-aware of just how much of an idiot he is so it's hard to feel much sympathy for him when he's obnoxious and moronic.
If you only know the American version, seek out the original. Seriously.