Lately, I (a 25 year old female gamer) have played Skyrim, Might & Magic Heroes VI, and Fallout 3, and I enjoyed all three.
I enjoyed Skyrim pretty much without qualifications; the only frustration I ever feel with that game are a lack of hairstyles I like and not being able to spend my gobs of end game money on world-changing events, such as opening a wildly successful business or rebuilding a temple. These objections are small, however, compared to the good points of the game.
I enjoyed Might & Magic Heroes VI, but I wish the faction balance was a bit better and that the game was less glitchy.
I enjoyed Fallout 3, but I felt the environments needed more variation and that some of the mechanics (repairing stuff, for example) were frustrating. Unlike with Skyrim, I only ever made one character, and I didn't explore every corner of the world. The early to middle stages of the game, however, were VERY engaging.
What is most important for me to enjoy in a game? In rough order of importance: Immersion, the right level of challenge, and an engaging plot/setting.
If I can't get really deeply immersed in a game, I usually lose interest in it fairly quickly. This is why I prefer games that let me play female characters, as I can get immersed in such a character better and more quickly. That said, I don't mind playing male avatars if the game mandates it, so long as I can get immersed in the character. Getting immersed means that the game needs to either provide passive, silent background cues for my character's personality (that I can then build on), or it needs to let me construct the personality completely. For example, I adore Persona 4, even though it doesn't let you totally create your character's personality; however, it does stay pretty far out of the way and takes a minimalist approach to giving you a foundation to work on, so it works for me. Games like Skyrim are ideal, because they're completely free-form (which adds greatly to immersion on its own) and let you totally dictate your character's personality.
I also need the right level of challenge: not too hard, but not too easy. Games with difficulty level settings are ideal, because then I can adjust the level of challenge to where I want it. Sometimes I'm in the mood to curb stomp my enemies, so it's nice to be able to set a game on Easy Mode and go nuts. More often I want an honest, meaty challenge, and I then set the difficulty level higher. (For the record, I have always been stymied by the idea of "girl games" that make the game easy; when I was a teen I played Zelda II, basically the hardest game I've ever played, through to completion, twice. I was, at the time, the most hardcore gamer I knew. So it's pretty fallacious to me to think that girls aren't as hardcore. Some are, sure -- I know some -- but some, like me, can really enjoy and even prefer difficulty.)
Finally, I enjoy games with an engaging plot and/or setting. In the case of the three games I listed for question one, none of their plots terribly engage me (though they're not bad, per se), but the settings really engage me. In the case of the Legend of Zelda series, which I enjoyed for a long time, both the setting and (especially) the plots engaged me.
In my experiences in the gaming world, there's as much variation among female gamers as among male gamers, really. My roommate is also a gamer, but she approaches games very differently from how I do.
There! I hope this helps you with your school project.