I've had this exact issue. Still do actually, as I'm still playing in the same game.
He literally trashed my first character concept in the game by changing the rules regarding magic item creation. I'll skip the details and just summarize by saying he allowed it at first, then changed the rules to tack on an extra 0 or two on the end of the gp cost for a magic item. As I was playing an artificer mage, this was a tad bit of a problem.
Multiple times I've caught him deliberately bending the rules to allow opponents an edge, and he himself has oft admitted he views the game as a GM vs Player contest. The other players in the group who are experienced with him have commented that they've never seen a character survive to 7th level. One got to 6th and was promptly retired in order to maintain the record.
I've caught him force feeding a situation to the players to force them to use certain critical magic items when he wanted them to, not when they would certainly need to. One poor character was killed due to a deliberate rules mis-interp concerning paralysis and drowning.
Just recently he tossed a full fledged Frost Giant, ECl=9/10 at us. It wouldn't've been too bad if we'd been a few levels higher... But for a party of avg level 3, this was a touch extraordinaire. Luckily, we only lost the first level ranger - the 5th level cleric had two hold persons ready and we survived - more on luck than anything. And this was a random encounter!
Strangely enough, I am still playing in this game. I've actually come to enjoy my new character to some degree, and I'm beginning to find amusement from how badly he strays in his gm'ing style away from what I've been used to as a norm. I've gotten to the point of acceptance, not ranting, and it's been a long hard walk.
I talked with him in the beginning - that did no good. I talked to the other players - that did little good other than letting us all agree on various elements of the complaint and feel a little better. In the end, since it's the only game in my neck o' the woods, I just learned how to accept his strange gm style. I'm now the unofficial rules lawyer though - as I struggle to keep him on the straight and narrow regarding blatant inconsistent rulings
We've handled it in a mature fashion so far. However, if a different game beckoned, or I had the chance to run my own again - I would take it with little regret.