While trudging through this game, which mind you isn't half bad when you give it a little time, I found an incredibly easy way to raise levels.  It's a bit tedious, but necessary unless you want to waste hours of your life building up for the final castle where vampires wipe out your part in seconds.

What you need to do is this.  Go to the inn where you enter into the catacombs (wine cellar).  Every once in awhile you'll receive a gold ring as treasure.  This item, when used, will break and cause you to double any experience and gold you receive for a particular battle.

Gather a bunch of these.  It takes time, but do it.  Now then, what you can do (and this applies to really any level where you're able to enter this area in the first place), is travel to any area with a boss.  While fighting the boss, chuck out the ring.  On higher level bosses, you'll get SICK amounts of experience, like I'm talking about 36K worth.  Do this once or twice at higher levels, and you're ready for the final castle.  Not sure if more than one ring will increase the exp.  I was going to try it, but feared it would negate the effect.

Finally beat it the other day.  Using this level raising trick you can get very powerful very quickly.  It was a good game overall.  The final castle was challenging at first.  Last boss was a bit of a wash though.