OK, so Larian doesn't care one iota or really understand how to implement a D&D system, so the question being "will it still be fun".
I have watched two videos of people, who like The Red Queen, have played into act 2; WolfheartFPS and Fextralife.
Fextralife is definitely less biased and reports that act two ramps up in difficulty, complexity of combat, and story. This is encouraging as every time I get used to Larian's combat they start to change the rules.
Normally rule changes are implemented very slowly and cautiously. First it is "Unearthed Arcana" and tested for months before it is canonized. Larian's approach seems rushed at the end, so we'll see.
By first hand reports though, Act 2 should be intriguing and fun.
As far as the story goes, it has its bright spots and completely falls on its bum in other areas. Grymforge, is stunning in its construction, but the story is a complete fail.
The Deurgar have no culture or character, neither do the deep Gnomes in sharp contrast to established lore.
Deurgar meme: Vulgar, uncultured, angry, and excessively cruel.
Deep Gnome meme: Bitter, vengeful terrorists, simpering, pitiful, and boring.
These races do have a rich cultural history and its a shame Larian didn't bother to do their homework, assigned them an evil tag, and wrote them in their own cruel image.
That whole area is a wasted opportunity.
Fextralife reports that act two is great story telling, this will be welcome.
I look forward to seeing the Githyanki encampment, the Harpers, and Moonrise.
As far as Multi classing, it is rarely worth doing, but their are a few great synergies.
I myself have decided to stick with Pure Valor Bard to be more durable and get my 6th level spell and attribute boost.