I thought it was a thoroughly enjoyable film. I liked that it was split in two with the chronological black and white and nonlinear colour sequences - it's a brilliant concept, which I've only seen executed somewhat similarly in an episode of Inside No. 9 before watching Memento. It could be a complete mess if it's in the wrong director/producer's hands, which is why we don't see it too much in film because I presume it can be quite complicated to work through.
Guy Pearce is an excellent actor, and the main character was super-rootable, mainly due to his condition. I expected Natalie to have more relevance to the eventual plot twist, but from what I'm reading since watching...she kinda did? I dunno, I think I should probably re-watch it to fully understand the motivation of her character. Teddy was a great character, and it was fun to work out his intentions regarding his relationship and motives with Leonard. I kinda saw through the whole Sammy Jankis thing, only because I thought it was convenient for Leonard to know someone with the same condition with him. There had to be more to it.
All in all, it was an entertaining film to follow with a good cast. Its unique structure helps it stand out and was cleverly executed.