This was previously used in the forums, but I felt pretty good about what I wrote so here's a history, I'll probably update it to make it more in depth.

Each series cannot really be compared to the others, in truth because they offer a different variety of gameplay choices.

Classic is a nostalgic and simple yet proven platformer series. It shows the roots of modern video gaming... without looking like pong. Hey, it's still fun too, right!

X brought forth the new era of megaman, with a difficulty spike, new characters, and more more complexity, the game was a perfect addition to the classic gamers looking for a challenge, although some might agree not all of the games are that great. *COUGH COUGH* Megaman X7

Zero and ZX were... well let's be honest, freakin' difficult, it was an even harder challenege, and most gamers would be happy to get a grade of D let alone survive a mission before breaking their GBA/DS. The series is amazing and the story closes the "trilogy" but its difficulty can be a major turn of/on depending on whether you like masochism.

Legends was admitingly a well recieved game in the megaman community, but not to anyone else. It offers an AMAZING storyline and a real in-depth game, but since it was one of the first 3-D games, there were camera issues as well as response lags. The series is definitely a highlight as an action/platformer/rpg genre.

Battle Network/Starforce is one of my favorite series so I'll try not to be biased. It's a kids game. It's a replica of pokemon, and at the same time, its not. While other games offer the ability to capture something, and use it and collect hundreds of these things, Battle Network took this concept and revolutionized and pioneered the real-time RPG genre (if it's not a genre it is NOW). Collecting battle chips is fun, as well as playing with your friends, but, if you aren't a perfectionist, you may think missions and chip collecting are tedious and boring. Not to mention the game definitely skims on a plot, heck it took them 5 games to get the plotline decent and then the 6th game totally shattered everything they had worked on.