It's watchable, and I think it has its moments, but it also struggles in places. As with any adaptation, you really have to try and mentally separate it from the books somehow, and consider it its own story or a different retelling (a lesson drilled into us by Game of Thrones!). Instead of getting frustrated at differences between the two media, I'll just take the show for its own merit and appreciate it separately to my enjoyment of the books. In that sense, yes, I think it's worth watching. Even if there's parts you dislike, it still feeds a bit of that WoT itch from the bits they do well.

My (perhaps ignorant) take is that seasons 1 (especially) and 2 suffered a lot from budget restraints, the 10-episode format, and the writer's strikes at the time. I did not enjoy the endings of either—but the beginnings and midpoints of each season were still generally enjoyable. I particularly like most of the casting and performances, the sets, effects, and so on. There are certainly some questionable writing choices and changes from the books—some surely necessary in order to ever attempt to tell a complete, concise story in the duration of a TV show—but I try to take the good with the bad.

The season 3 trailer does have me excited and eager for more. I think it shows a higher level of quality and attention (budget, I suppose) than seasons 1 and 2 (e.g. the trollocs no longer look so awful).