If you ask me, three of the same game on one system is usually overdoing it. That being said, older systems had longer lifespans, so it happened more often.

Likely Super Mario Bros. or Ninja Gaiden on the NES. Definitely Mario 1-3 if we're comparing how the series ended. (NG3 was the worst, even if SMB2 was an acid trip)

The original Metal Gear Solid trilogy was amazing. I like how it takes itself seriously, but not always(some of the cut-scenes had me rolling on the ground laughing).

That's another great trilogy, though I found the third one to be a bit too weird. The supernatural stuff just seemed out of place in an historical setting. MGS4 was perhaps my favorite though, that or the original.

Mega Man X1-X3 on the SNES! All kinds of awesome!

I can't believe no one said Metroid Prime trilogy!
Thats mine though.

The 3 Paper Marios of course!

Jak & Daxter Trilogy FTW

Metroid Prime

Um. Look at post 7 then tell me what you think.

Too Human, I know its not done but I lo... YEAH RIGHT!! Seriously my favorite trilogy is the Metroid Prime games. I don't really count the NES mario games a trilogy and I'm pretty sure Paper Mario will continue.

The first 3 Sonic games.

For me only Metroid Prime comes to mind. Pikmin and Mario&Luigi will probably be added ones their part 3's hit europe.

God I'll sound like a right killjoy here, but a trilogy is a story that spans three volumes - a beginning, middle and an end. Mario and Sonic games are automatically disqualified because they clearly span many volumes (Sonic Adventure is clearly a continuation from Sonic 3) - it's like saying the first three episodes of Lost are a trilogy.

One series I can think of that could be classed as a trilogy is Streets of Rage ... wait how sad am I typing this at 3:30 in the moring? I'm off to sleep.

First three Metal Gear Solids, although they leave it very open for MGS4.

Shenmue. Don't tell me they're not making a third. I will never accept that. It has to be a lie, they would not do that to us.

@Madgear
http://dictionary.reference.com/browse/trilogy

Games can be related by theme or form. Story is not the only possible uniting factor for a trilogy. Sonic or Mario 1-3 would each be a pretty clear trilogy as each builds on the same formula very closely (well, for Mario, that would be true if you count the real sequel rather than the US version).

• NES Mario trilogy
• Metroid Prime
• Rayman 1-3
• GBA "Metroidvanias"
  And, once the 3rd entry gets relesed, God of War, of course!

Three games in a series doesn't make a trilogy...

Trilogies have story connections, Paper Mario isn't a trilogy, Super Smash Bros. isn't a trilogy, excetera.

I haven't played the Soul Blazer/Illusion of Gaia/Terranigma series but I'd assume they'd rank highly.
I'm not really a Metroid type of guy, but the Prime trilogy is great (haven't played 3)

Well, there's not a lot of proper trilogies out there...

OOH OOH THE LEGND OF ZELDA TRILOGY!!!!!!

Actually,

Sonic the Hedgehog 2, 3, and Sonic & Knuckles

my trilogy of choice (as well as the original sonic the hedgehog game), are actual trilogies as they are all connected in events, characters and themes. The 3 that I'm nominating actually take place within hours of each other in the story, as seen in the cutscenes for the games, especially in the second one.