I'm an SGU fan. I always considered the 1st two series kind of a cut rate Trek. Cheap actors, cheap FX... No offense if you liked them, but I just couldn't get into these shows at all. To be fair, I'm basing that on watching maybe 6 or 7 episodes of SG1 and SGA.
But after watching SGU on a whim, I was impressed. They have assembled a really top notch group of actors (for the most part) and have really pushed the FX forward a great deal. I like that there is more focus on the characters and their relationships than techy type stuff. I like that for the most part there isn't a good/evil set of characters, everyone has some good qualities and some bad..just like real people.
I've heard that some people consider the show dull because there haven't been many action sequences. I like that though. I have more reason to care about the characters, so when something dangerous happens I actually give a crap about it.
I also like that in a way, this seems to be a standalone series. I haven't felt lost at all from not knowing much about the previous Stargates. Great place for new fans to jump on.