I am not terribly good at assessing combat aspects of games so hopefully someone else can pitch in.
As for the combat in FO4, the shooting mechanics were improved significantly over previous fallout games.
There is a decent selection of weapons in the game, and you can find legendary versions of weapons as rare drops, which give the weapon
(or armor) a stat boost, and sometimes a secondary effect like fire or explosive damage.
You can still use VATS if you prefer, it is slightly different than the past, and enemies will move slowly while you are lining up your shots in VATS.
Playing a melee character is viable, especially in conjunction with certain drugs.
Playing mainly through VATS is possible, and there are perks to help with it.
Character progression is handled via perk points, and there are many useful and different perks to choose from. (some are better than others...)
Power Armor was revamped completely from previous games, and now you "drive" the suit rather than wear it like any other piece of armor.
It offers a number of advantages like high damage resistance, high radiation resistance, improved melee and carry capacity, and nullifies fall damage.
You can attach mods to the torso piece depending on your crafting abilities and resources, the best ones are probably the stealth system and the jet pack. You can attach some useful mods to the helmet as well, including a HUD with an IFF system that will paint organics NPC's in red. (somewhat akin to "detect life" spells)
There are mods that modify everything, including JetPack fuel (stamina), the IFF system to only paint enemies, and more.
Another notable advantage of using power armor is immunity to a Deathclaw's grab sync-kill.
There are also some disadvantages to using power armor constantly.
The most obvious is the need to use special power cells as fuel; the armor is also noisy and heavy and will make it difficult to sneak unless you max out
all the relevant perks; you can't swim with the armor, and should you go into water you will be forced to walk on the bottom, and due to low visibility
and difficult terrain it sometimes can be difficult to find your way back out of the water.
Crafting and building is fun for awhile, but can get tedious, especially the management of multiple settlements and their occasional needs.