I went to Fenway while working in Boston for a few games in the summer of 2012, and enjoyed it so much that I took my kids back to see a game in 2013. Great, historic park. Every seat feels like you can catch a fly ball.
A few tips...
1) If you aren't staying in the city, I found it's easier to park at the end of the Green line and take the train to Fenway. Very convenient, trains every 10-15 minutes both before and after the game.
2) If you have kids, go early (around 5:30PM) for batting practice. When we were there, it wasn't too crowded, and we were able to get right up against the fence in right field. Plus it gives you a great view of the park from up close.
3) Double check your tickets to before buying as there are a lot of obstructed views in the park.
4) The food choices are a bit limited. If you like hot dogs, they are very good and served on white bread, which is different. Grilled sausages are also awesome and they grill peppers and onions at most of the stands.
5) If you go with kids and they get bored, there's an outside area that you can access and still get back into the park that has some free games like a pitching area that times the kids pitches. Most parks I've been at charge for that, at Fenway, it was free.
6) If you go with just adults, there are quite a few bars that are open before / after the game in the local neighborhood. All seem like fun sports pubs.
7) If you want a souvenir hat, you can find them outside the stadium for $5 each. I found one vendor near the Fenway Green Line stop, and another towards the arena where the Bruins play (TD North?)