I haven't played any Metroid games since Super Metroid back at release. I recently got heavy into GBA gaming with my Micro and after being non-wow'd by a few games, I decided to give Metroid Fusion a try.
I am officially wow'd.
At first it felt a little weak. The combination of the map and no hidden stuff made it feel kind of bland and easy. After a couple hours, the game really picked up. The discovery of bombs brought back the old school Metroid OCD inducing "bomb everywhere" mentality and many, many secrets. The map is actually useful while not making it too easy. The way secret passages are marked (and not obviously revealed before discovery) on the automap is perfect.
The challenge quickly ramped up. I am reaching the end (I believe) and so far there have been two bosses that I thought "holy shit, this is impossible". After trying and trying, I finally figured out the tactics to use and then they were easily defeated. The most recent boss (don't know the name, the gravity related one) was so hard at first, that after trying many times, I almost gave up to hit read a FAQ or something (I avoid all forms of spoilers/FAQs/walkthroughs for games I am playing through). I kept at it and despite much cursing and frustration, when I finally figured out the pattern, it was so satisfying.
It has been a long time since I have been sad when a game is complete, but I predict I will feel this way once I am done.