Short non-spoilery review: that was marvellous!
Slightly longer non-spoilery review: there wasn't a single bit of that film that I didn't think was excellent. Witty, thrilling, action-packed. Some sparkling dialogue, didn't take itself too seriously (pure Joss, in other words. The final sequence in New York was perhaps a bit reminiscent of the end of Transformers: Dark of the Moon but done a thousand times better (can Joss take over the Transformers franchise from Bay, please?). So yeah, a great film, and I speak as someone who went in with no prior knowledge of who these Avengers were (apart from, "they're superheroes") or what to expect. Hugely recommended.