As was pointed out in an earlier reply, the secret to challenging players is tactics. Remember, magic has been around for a while, and anyone who has ever been hit with it learns really quickly how to avoid it the next time. A couple of tried and true tactics that every NPC should be using...
1) Avoid "fireball" formation... ie- spread out to avoid everyone getting clocked by the same spell.
2) Keep a reserve and/or sniper out of the fight on "mage detail". When magic starts flying, he starts shooting at anyone not holding a gun. A varient I've used is keeping someone in a parked car (with tinted windows), and having him run over any mage'y-looking people. I've used this so successfully that one mage in my group started dressing as a street sam (even so far as wearing a cyberarm sleeve and shiny contacts) just to avoid getting shot at during firefights
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3) Flashpacks or flash grenades. Visual penalties = casting penalties.
4) Smoke cover (the Renraku Evening Mist is great for this). If the mage can't see you he can't cast on you either. Remember, every meter of smoke gives cumulative penalties, so being a couple of meters in a smoke cloud makes you immune to magic (and having an ultrasound sensor with image enhancement, or a radar implant allows you to see everyone clearly while staying protected from mages).
5) Guardian or Plant spirits. Both of these have the Magical Guard power, so can be used for spell defense for an entire group. This may be beyond the price range of your average street gang, but every corporate security team that doesn't include a mage would have one of these spirits on remote service.
6) Opposing mage. What's good for the goose is good for the gander. Let the party eat a Control Actions spell every once in a while... it builds character after all.
The best way to convince a player to round-out a mage, however, is to let them realize that the game isn't about all-combat all the time. If you don't have any social or information-gathering skills, you'll be sitting around bored for most of the game until a fight breaks out. So make sure the leg-work parts of the game are very fleshed-out and involving, and pretty soon even the most unbalanced character will start being smoothed out so the player can get in on the fun.
Jim
