I'm not really sure what kind of game, or what effects you want in your game. So I can't really say whether a standard 2d engine would be right for you, but there are some valid reasons to use 3d for a 2d game. Even some 2d cartoons are made with 3d software, such as southpark(made in maya).

there are basically two approaches you can use to make a 2d game. use a gui to create your game in a already 2d flat plane. for this you'd use something like gorilla or cegui or mygui or whatever flavor you choose. I would however say you will want to avoid using overlays as some have suggested, as the batch count would end up far too high. This method leaves you with the least number of advantages that I can think of over using a standard 2d engine, and wastes the most of ogre's power. downsides here are that you still need to do things such as create a sprite class to handle animations.

the other method is to place all your sprites on geometry within the scene. you'll use something like billboards here. here you can either fake depth like you do in a standard 2d game, or can create some assets that are actually closer or further from the camera, though most actual game elements should probably be the same distance from the camera, that will mostly depend on your game logic though. things like cityscapes in the background, or branches up close in a jungle scene are fair game. and depending on the look you are going for, you could set the camera up as either an orthographic camera to keep a pixel accurate scale everywhere, or take advantage of the cameras natural perspective.

another thing you can take advantage of using ogre is the bone system to make paper puppets, so instead of doing a full drawn sprite, you can easily rotate limbs(though which looks better will still strongly depend on your art skills).

you can toss in some actual 3d in now and then. sometimes you just want that powerup or whatever to look like its rotating, and well, you can just make it rotate in 3d without worrying about drawing to look like it. enemies or obstacles can come onscreen from 3 sides instead of 2. its also possible to have a 3d landscape with 2d sprite characters(such as final fantasy tactics and I believe a number of fighting games) sometimes the problem with 3d is that sometimes the poses you want, just don't work when on an actual model, having 2d sprites lets you push those poses much further sometimes... anyway, think I'll stop rambling now. just wanted to add my 2 cents to all the people that keep trying to say don't waste your time. there are valid reasons, and cool things you can do that are more difficult in a traditional 2d engine.