I played the first Metroid prime (~80%) on game cube and loved it. Back then I gave up on this game as I could not solve the last riddle and was not familiar with online strategy guides.
Since Prime series came out as Trilogy on Wii, I feld obligated to give it another shot and here is what I experienced.
METROID PRIME 1
-BLOW JOUR MIND: The environment, the scene and the experience you get through them is just amazing. I still can't believe that they created such effect using gamecube technology. JUST MARVELOUS.
-Gadgets: Different beams, missles upgrades, suit upgrades, double jump, powerbomb, combo attack, morphball upgrades, grapple beam. JUST AMAZING.
-Story: This is what I like. For those who don't care much about the story, you don't have to read it all. But to those who do, everything will be explained in the FINEST DETAILS. VERY WELL DONE.
-Bosses: Again very creative. The final battles are probably THE MOST CREATIVE in the trilogy.
-Length: Areas are fairly huge. If you go after majority of items which is highly recommended as final bosses can be tough, it will take you a while to explore them all.
-Bonuses: More you explore, more endings you get to uncover. EXTREMELY REWARDING EXPERIENCE.
- LOTS OF BACKTRACKING: Without a guide, this can be really irritating. Even with a guide, I hated how you have to back track a lot of areas in the ending.
- Annoying double jumps: Some upgrades require morphball double jumps. Failure to do so will punish you (harshly at times.
-Too many words: Story is really good, but I wish they had more cut scenes.
METROID PRIME 2
-COOLER THAN THE 1st GAME: The environment, the sceneries, the characters and theme are darker than the first game (and by that I don't mean they are black in color, they are more shady, the tone is a bit more serious).
-Gadgets: Cooler beams, awesome visors (actually useful in this one), missles, powerbombs, grapplebeam, PLUS MOST IMPORTANTLY YOU HAVE SCREW ATTACK. JUST LOVE IT.
-Bosses: While final fight was not as great as 1st (Still pretty good), the rest of the bosses are THE BEST IN THE TRILOGY. I mean the first time you encounter dark Samus is just EPIC. And other bosses especially in the dark world are very fun.
-Length: Greater thanks to dark world
-Bonuses: same is first
-Same as first, LOTS OF BACKTRACKING, ANNOYING DOUBLE JUMPS, OTHER DIFFICULT MANEUVERS and TOO MANY WORDS
-Dark world is a wonderful creation, but as you lose health while playing in it causes constant stress in your mind and can make the experience torturous in the beginning. Don't worry, towards the end you get upgrades to counter it.
METROID PRIME 3
-A WHOLE DIFFERENT VIBE: While the first two game are mainly solo mission where don't get to interact that much with other living beings, this one is completely opposite. This game has quite a few interesting characters with awesome abilities (Unfortunately not playable though)
-Gadgets: Again newer beams and other goodies.
-Hypermode: LOVE IT. New and most welcome addition. Don't want to spoil it for you.
-YOUR SHIP IS ACTUALLY USEFUL: HA HA play to find it out.
-Very Creative use of Wii mote: Yup. You will be using wii mote in different ways to perform different actions. I liked it.
-Bosses: They are good. I like their abilities more than the fights themselves. Like in 1st and 2nd, you can't just shoot them to kill them, you'll have to use your nugget.
-Length: Only slightly longer than the first (definitely shorter than second)
-Bonuses: Same as first two (Love the 100% ending though.
-Same as first two, LOTS OF BACKTRACKING, ANNOYING DOUBLE JUMPS (most annoying of trilogy, horrible), TOO MANY WORDS
-NO POWER-BOMB and NO COMBO SHOT ...... WHAT THE HELL???
-Not that Metroid games are that adult rated
-Easy to miss USING AN UPGRADE: Upgrades in this game are very useful, but if you are not reading their details, you won't utilize them fully making the experience dull. HIGHLY RECOMMEND USE GUIDE OR EXPLORE YOUR ABILITIES A LOT
-Even with Wii's inferior technology, the graphics are updated (look pretty good on my HDTV).
-The use of wii mote makes shooting and other actions easier and fun (While making few actions difficult and annoying).
-As for the trilogy itself, it's pretty amazing. While all three games do have some setbacks as described above PROS OUTWEIGHS CONS BY A HUGE MARGIN SO BUT IT AND HAVE ~50-80 HOURS WORTH OF BLAST.