It was. And an incredibly important one too. It played an important role in the original GameBoy's success.

I think Wii Sports just blew away Tetris, but Tetris blew away everything else ever.

Smash Bros. Melee, Halo 1, Super Mario 64, and Zeldas Twilight Princess are the best launch titles in the history of all gaming.

On a whole-market level, I'd rate the top 3 as:

1. Wii Sports (Wii)
2. Super Mario Bros (NES)
3. Tetris (GB)

I can't really rate it on a personal level, as the Wii is the only console I've ever gotten near launch. The game I got my PS1 for (Xenogears) was not a launch title, nor technically was the game that I got my PS2 for (FFX). I got my GBA SP long after the system launch and didn't get any title older than LttP for it. I guess Super Mario 64 DS counts for my DS (and I did play it quite a lot). My PSP's initial line-up of games was a total joke before Valkyrie Profile came out. And I do remember Super Mario Bros being our most-played NES game back in the day.

So... I guess if pressed, my personal favorite for a launch title was Super Mario 64 DS, even though that wasn't the game I got my DS for (Dawn of Sorrow was).

 Melee wasn't a launch title, was it? At least here in Europe it wasn't. 

No, Melee was not a launch title. It came out one month after Gamecube launch.  In NA anyways.

Yeah, I thought so. Europe was the same.

 No it wasn't.

The best launch title ever, to me, is Twilight Princess.

Launch title, not best game.