Is mechanicus fleet better armed then other imperial fleets?
They have superior technology, like actual autoloaders instead of using slaves to load the skyscraper sized shells into guns (thanks 2nd edition!) and yeah, they are pretty much better armed.
Why marines are not allowed to have super heavy tsnks, titans and battleships, like they used to in great crusade?
Because of Horus Heresy, the same reason why Imperial Navy and Imperial Guard is now split, instead of being one huge Imperial Army. They just don't want one branch to have all the cool toys, as in Navy doesn't have ground troops, Guard cannot move without help of Navy and Space Marines can do basically everything but they lack the heaviest cannons and their ships are purposefully weaker than Imperial Navy ones, so they can be rekt easily.
How life is prolonged in imperium?
Genetics, chemical rejuvenation drugs, mechanical augmentation, warp fuckery.
Are leman russes with subatomic charges awesome?
Leman Russes are all awesome.
Are there any good stories written from machine spirit/ tyranid perspective?
I don't really know of any story like this that isin't fanfiction.
- Armageddon
If you ever played Panzer General or Panzer Corps or maybe the old Final Liberation, this is kinda how it is. It's basically large scale tactical combat with elements of strategy, but remember that it's built on Panzer Corps so this is a game where you basically follow orders and there isin't a lot of freedom (though you do sometimes get to choose where you're fighting next, but it's usually harder/easier mission selection) other than how to setup your units and use them and whatnot.
Depends on your taste a lot.
- Regicide
Coolio Wh40k chess, has great kill animations but in the end it's just Wh40k themed chess, and no special rules can really change it. Fun, but IMO not really worth it. Maybe there will be more races in future, since now it's like two Space Marine chapters and some Orks.
- Dark Nexus Arena
It's a MOBA, so, if you like it, you'll like it, if you don't, you'll hate it. I haven't played it though (maybe if they add an Imperial Guard related
hero veteran in future), but it apparently is pretty fun. Also you can play as "KHÂRN THE BETRAYER", which is something.
- Eternal Crusade
Buggy as fuck but pretty cool Wh40k shooter. Think wonky multiplayer only Space Marine with a lot of promise but not really a lot of stuff yet. Basically all of the last three things seem to be very unfinished.