A thoroughly entertaining sequel that delivers on all fronts!
I loved the first Thor film.
He is a very difficult superhero to bring to the screen and his comics were never all that great as he didn't receive the same kind of quality treatment as other more popular Marvel characters.
Luckily, Branagh & Whedon are both great Directors and the casting was superb - not just the main characters of Thor & Loki but also Odin, Frigga, Selving, Hemdall, Sif etc. Even Portman wasn't bad as Jane Foster :)
These strengths made for an exceptional first film but I honestly had no idea how they would follow it or how they could progress Thor's individual story (outside of Avengers).
Taylor has somehow carried these strengths (along with the same look & feel) into the sequel but also managed to expand Thor's universe, further developing the main characters - all this while keeping things light hearted and entertaining. A very ambitious & commendable achievement!
Also, from the 'after credits' scenes and the ominous "THOR WILL RETURN" it appears Marvel has much more already in the pipeline (they're clearly planning several years ahead with these films). We can expect to see Thor in action on an even larger (cosmic) stage - one that comic book fans in particular will appreciate (Infinity Gems anyone?!)
In the same way that T2 was a great sequel to Terminator (or Aliens was to Alien) this film is definitely a worthy successor.
This is easily the best CBH film of the year.
Go see it - it's awesome! :D