The big problem is that your DM is changing things and not giving you any notice. I have no issues with house rules, and my current game has all kinds of bits and peices: but the players need to be on the same page.
Flat-out ask him for a Word document or something that has his rules changes on them. Tell him you appreciate his right to have to make judgements ont he fly but you want to have the bare bones of the system in front of you so you have something to refer to during game to help make decisions about actions etc. If he resists giving you something, this is a gigantic warning sign, and not something I would ever tolerate. You need to call him out on this, and ask him what the difference is between him spending a token to save a bad-guy and just deciding that something a player does doesn't work because, erm, he didn't plan on it. DM Fiat should be acknowledged by him as such, and not dressed up in a rules system he doesn't explain to you: and you can't be expected to ever win a combat if you don't know the rules you're working within are.
Furthermore, there seems to be a certain degree of "bait and switch" going on here. As others have said, WFRP, True20 and many other systems would give him a game system more suited to what he wants to do, but instead he's playing heavilly house-ruled D&D. IF he's aske dyou to play WFRP you'd have come in with a set of expectations and had them fulfillled - here, you came for D&D and are a bit unchuffed as to how very different it's ended up. That's not unreasonable of you, and a GM should make a better effort when starting a game to make sure everyone is ont he same page as to what it would be like.
This sounds a bit like your GM is "damaged goods". You said he changed shooting due to a bad experience with a past group that "broke his plot": I've had a dire group that went crazy on me before, and afterwards I'll admit I ran my next few games with a lot harsher temprement to try and stop the same thing happening again. If your GM has the same fears, he has probably built this campaign and rules tweaks to solve the problems of that game. "Oh no, my BBEG got shot from long distance!" "Oh no, a two-handed Power Attack killed my Vampire"! "Oh no, they got this magical flaming sword I hadn't thought they'd ever retrieve from the Orc Warlord!" He's potentially over-compensating for the issues of a previous campaign, and you're taking the brunt of his anger at another gaming group.
The best thing I can think of is to speak to the other players. If they're happy with what's going on, then that's fine - but you have to ascertain if any others would rather be playing a more by-the-book game, and if your dislikes are shared by them. If not, then perhaps you politely retire if he's unwilling to share the rulebook with you; if so, then it's time to have a chat with the GM and make it clear that multiple of his players are underwhelmed. Be polite, but be firm: he may not realise it's a problem and expects that his plot or whatever is making up for it. To all accounts, it is, but things like the DMPC and the mega-punching Vampires are going to continue to grate.
Flat-out ask him for a Word document or something that has his rules changes on them. Tell him you appreciate his right to have to make judgements ont he fly but you want to have the bare bones of the system in front of you so you have something to refer to during game to help make decisions about actions etc. If he resists giving you something, this is a gigantic warning sign, and not something I would ever tolerate. You need to call him out on this, and ask him what the difference is between him spending a token to save a bad-guy and just deciding that something a player does doesn't work because, erm, he didn't plan on it. DM Fiat should be acknowledged by him as such, and not dressed up in a rules system he doesn't explain to you: and you can't be expected to ever win a combat if you don't know the rules you're working within are.
Furthermore, there seems to be a certain degree of "bait and switch" going on here. As others have said, WFRP, True20 and many other systems would give him a game system more suited to what he wants to do, but instead he's playing heavilly house-ruled D&D. IF he's aske dyou to play WFRP you'd have come in with a set of expectations and had them fulfillled - here, you came for D&D and are a bit unchuffed as to how very different it's ended up. That's not unreasonable of you, and a GM should make a better effort when starting a game to make sure everyone is ont he same page as to what it would be like.
This sounds a bit like your GM is "damaged goods". You said he changed shooting due to a bad experience with a past group that "broke his plot": I've had a dire group that went crazy on me before, and afterwards I'll admit I ran my next few games with a lot harsher temprement to try and stop the same thing happening again. If your GM has the same fears, he has probably built this campaign and rules tweaks to solve the problems of that game. "Oh no, my BBEG got shot from long distance!" "Oh no, a two-handed Power Attack killed my Vampire"! "Oh no, they got this magical flaming sword I hadn't thought they'd ever retrieve from the Orc Warlord!" He's potentially over-compensating for the issues of a previous campaign, and you're taking the brunt of his anger at another gaming group.
The best thing I can think of is to speak to the other players. If they're happy with what's going on, then that's fine - but you have to ascertain if any others would rather be playing a more by-the-book game, and if your dislikes are shared by them. If not, then perhaps you politely retire if he's unwilling to share the rulebook with you; if so, then it's time to have a chat with the GM and make it clear that multiple of his players are underwhelmed. Be polite, but be firm: he may not realise it's a problem and expects that his plot or whatever is making up for it. To all accounts, it is, but things like the DMPC and the mega-punching Vampires are going to continue to grate.