I've read a few reviews here saying it's the worst thing they've seen all year. I think that's a shame. This is not an Oscar-winner by any definition, granted, but it's not the low point of 2010's cinematic output either.
I accept the point that Sam Worthington isn't a good enough actor to warrant the hype, but he looks the part, and it works for me. The characters, although portrayed by decent actors, are shallow and/or predictable (a conversation on Charon's Barge reminded me of all that was crass about the Airport movies), so rather than rooting for them, you're just left trying to work out in advance which one will die in the next battle. But this isn't attempting to be educational or otherwise "worthy" in the Schindler's List vein... it's meant to be entertaining, and it manages that.
As a visual spectacle, it's worth watching, although movie effects usually translate poorly to the small screen. It's fair to say the Kraken is woefully underused, and the scorpions are average at best, but everything else passes muster, and the Pegasus is gorgeous!
Ultimately, I think this film isn't what the makers hoped it would be, but it isn't a stinker. It's always going to be compared (probably unfavourably) with the original, and rightly so, but it's still an enjoyable way to spend a couple of hours.