Empire Wizards are maybe some of the best wizards in the game. Why? Because they can chose from any of the standard lores! They can do anything!
But don't go crazy. The magic rules in the latest edition of Warhammer are pretty restrictive on the number of wizards you can get away with. There are only so many power dice to go around and I think a fourth level and a second level is about where you want to be aiming. Any more and the third wizard tends to hang around, wondering why he was invited considering nobody's passing any dice his way.
I love my wizard on his flying carpet. But at 50 points for the carpet (from the Warhammer rulebook), is he really worth it? I don't think so. For me he's more of a cool factor thing. I've cut him from my recent army lists.
Choosing the magical lore can be tricky. I recommend having a good thorough read of all the lists and settling on the one that has the most spells that match your playing style. It's a shame spells are chosen randomely. I'm a huge fan of the Transformation of Kadon spell; but I don't really like the other Lore of Beasts spells. The number of games I've chosen Lore of Beasts hoping to get it and ended up with some other crap...
Maybe I think I could run my wizard forward and cast enhancement spells on him to make him good in combat. But then, what if I fail the roll or it gets dispelled? That's the problem. I keep choosing that lore in the vague hiope of accomplishing something but I never do.
The Lore I've had most experience with (and has never let me down) is the Lore of Fire. It's simple, straight forward and easy to use. There may be some sneaky stuff in the other lists but give me good old-fashioned blasting power every time! And the Fulminating Flame Cage is ace for annoying my opponent by freezing one of his units in place at the risk of them being damaged.