The weirdness comes almost entirely down to the second one, which is a full-on Tom Cruise megalomaniac vanity project that's such an left turn it throws the series so far off its axis that they had to spend the next couple of films trying to reestablish what the hell the series was even supposed to be.
I never saw the third, but the last 3 mostly ditch the 'auteur' thing they originally had going on and settle on a formula where they tick off a bunch of series boxes in slightly different arrangements each time: you'll have your big centrepiece stunt(s) performed by Tom, some kind of heist setpiece, twisty turny double cross bits where at least one person ends up pulling their face mask off, and your standard assortment of fights, car and foot chases etc.
To be honest they're probably better off for it. The first is the only one that feels in anyway like a 'real' thriller film, but the new ones are reliably entertaining superspy nonsense. The whole helicopter chase sequence at the end of Fallout was, I have to say, FACKING AWESOME.