This is why a really good boom operator is so important.
There are a few things you can do to try to lower the noise floor in the recordings, such as multiband expanding, noise reduction, etc... but as far as reverb goes, there's not a whole lot you can do. As far as the recordings sounding different, do you mean the timbre of the sound? The frequency content? The reverb? If it's the frequency response and timbre, you can work with that a bit with compression, eq, and similar tools. With the reverb, again, you can't really take any out, you can only add reverb. You could try dirtying up your closer shots a little bit to make them match a bit more.
Also, remember that perspective sounds for something too. If you have a wide shot with a little bit of reverb, then a close up with a lot less, that can be ok, as long as the difference is within reason, because it's how we actually perceive things in real life.
But again, I stress that this is where an experienced boom op comes in handy. A good boom op will be able to work with the room and grab a good angle and get the best sound possible out of a situation. He can also recommend when wires are absolutely necessary.
In the future, try to grab a boom op that has at least some decent experience. If you can't get one for whatever reason, there are a few things to know about boom placement:
Ride the frame line as close as possible.
With a good boom mic, even rotating it an inch can change the sound. Listen to the sound you're getting to make sure you're getting mostly dialogue, and little room noise. If you're getting reflection from a wall, articulate the mic so that the wall is at the side of the mic instead of in front of it.
ALWAYS aim the mic at the solarplexis. NOT in the general direction of the actor. NOT at the actor's mouth, head, face, etc... ONLY the solarplexis. FYI, the solarplexis is basically the sternum.
Avoid booming from below if at all possible. If you aim up, you open yourself up to a world of problems.
Let me know if you'd like me to expand on anything or explain anything differently.
Oh, and as the other guys said, ADR is always an option, but unless you have VERY talented actors, it's probably not going to work out well. ADR lacks the emotion and conviction of the moment. All of the concentration of the actor goes into the timing.