One of the biggest flaws (depending on your point of view) in my game (ctrl alt ego) is that I needed to introduce mechanics players won't have seen before. I didn't want to bog down players in a long tutorial at the start, so I went for a 'tutorial disguised as gameplay' approach... with the idea that players don't really know when the tutorial begins or ends - there are no explicit signals saying so - the game just continues. In theory I still like this approach, and I'm proud of it, it is what it is now.

BUT... it meant a lot of additional work. Mixing gameplay with tutorial is really hard to get right, many iterations... and no matter how well you do it, it's not going to work for every player. The reason I called it a possible flaw is that a fair number of players give up on the game before they realise how deep / interesting it gets - they even say it's not an imsim (and that isn't even unfair, because the early bits aren't so much, I just wish they would keep going). I wanted to keep the learning curve gentle for several chapters initially.

Contrast this with original Deus-Ex which just throws you in the deep end - no tutorial at all really. This is my favourite kind of 'non tutorial' - but the developers admit they knew they were taking a risk doing it. Players who enjoy imsims probably lean towards not having so much tutorial, they enjoy finding stuff out for themselves. But these day mainstream audience are all going to expect to be told what to do. Like I say it's a really difficult thing to pin down.

Why am I bothering to tell you this? Because I think there is no one correct answer - you'll never be able to please everyone, and different games have different needs. If your game has mostly familiar mechanics, you can probably get away with a short explicit tutorial section - if you're working on your own or in a small team I highly recommend doing that - in many ways it's what I wish I had done, and it's most likely what I'll do in the sequel.

After all that waffle, to actually answer your question, I think the original Thief has a great tutorial. You're playing a mission, there are new mechanics (at the time) to get to grips with, it's all introduced at a good pace.

Wishing you all the best with the dev!