Climbing the tech tree, unlocking newer and deadlier toys, and building up your army is one of the most satisfying parts of strategy games. Halo and RTS fans should obviously get the game but I expect more from a sequel, the game´s campaign even finishes in a paid (!) DLC which stinks, so get the HD version of Halo Wars 1 first. Halo Wars 2 units every Spartan, tank and Sentinel. That one also relies on real money to buy new cards, which serve as your units. The campaign is still fun enough and the multiplayer modes are also solid, even if I can't judge how balanced the new Blitz mode is.
You don't even get to face the game's antagonist at ANY point, meaning that Halo 2 doesn't have the worst ending in the series anymore and Halo 5 now doesn't have the worst plot. You again only play as the humans and nothing happens in the story till the final cutscene. The campaign´s content on the other hand proofs as surprisingly restrictive. The technology is very impressive too (the army size in the last level is staggering!) and the controls are very fluid. The basic idea for the plot is strong and could work as a standalone Halo film.
The sequel sure took a while and everything seems great at first. Strategy games had a touch life on consoles till the 360 came along and the prequel ended up being one of the better such games of its time.