EDIT: I've now beaten the game, this is a finished review.
How do I say this and keep it simple? Well...to put it simply, I'm just not having a whole lot of fun with it. It's not like other games, like Halo 5 for example, where I started having fun the minute I played it. I keep playing Gears 4 and wondering, "Okay, when does the fun start?". I've been on the Gears bandwagon since basically the beginning of the franchise, and for some reason I'm just not feeling this entry. I shouldn't have to wait for the fun to start in a game like this, the fun should be happening pronto, ASAP.
The campaign is not that impressive, from any given angle. So far, the story drops you into the familiar Gears world with a little bit of flash, a hint or two of different ideas, and then the new faces you've seen in the promo material, but overall nothing too dramatic or exciting. The frame rate also leaves something to be desired; the frame rate in the campaign makes the graphics look slow and muddy, and it's very noticeable, something I never noticed before while playing other single-player Xbox games. Maybe it would look better on a high refresh-rate monitor, instead of just a basic TV? I don't know, I'm spitballing here. The graphics aren't that much different from previous entries either, it's shockingly familiar-looking for a brand spanking new entry on a next-gen console. I've even seen some low-resolution loading, and at close distance too! For a platform exclusive, that's a little bit sad (excuse me, it's also available on Windows 10 for some reason).
UPDATE: The first act of the game is truly one of the most boring things I have ever played. But, it gets way, way more interesting once Act 2 rolls around and you meet Marcus again, as you've seen in the trailers.
As it stands, I pretty much hate the multiplayer. The free DLC packs they gave me when I bought the game feel all but worthless to me, since 90% of it was "Bounties", which are just glorified challenges to net you more of this game's version of in-game currency. The other ten percent was an unimpressive weapon skin, a cheeky Crimson Omen sticker, an emblem, and a playable character that I neither knew or wanted to play as. One thing about the emblems too, it's kinda funny actually: nobody actually sees your emblems. Nope, the only people that see your special snowflake emblem are the people you invite to your party, so that big thing about "you get a special emblem for playing the old Gears games" is a little silly in hindsight. What is it about game developers that keeps them from realizing that customization is a huge plus? What, I'm choosing this neat little emblem for my own enjoyment? No, I want other people to see me being different while I'm being different, dangit!
It takes longer than it should to find a match. The multiplayer is shockingly difficult too, much harder than what Gears 3 was. I never felt like I sucked this bad in Gears 3, I did reasonably average at the minimum. My friends say it seems like old-school Gears, but personally I think it's lame. You drop into each match with literally a fraction of the last few games' selections for your loadout (everyone is using the same weapons, and you don't even get a proper grenade, you get smoke grenades), and the game modes are basically just different flavors of deathmatch. And I hate to say it, but the controls kinda suck too, I've been experimenting with the aim and look sensitivities, and I can't seem to get it right. The characters' movements and the gunplay both feel slower and lesser-than compared to how I remember Gears of War 3 feeling, which is the last Gears game I played. My team keeps getting smoked too, and badly, and I can't help feeling like the game has let me down. Even the Lancer is hard to get any kills with; everyone in the match is using the Hammerburst because it's deadly accurate, I'm getting sniped from across the map with an assault rifle. Oh, and the maps haven't impressed me yet either, so far they feel small and simple: just a spawn on each end and a common area in the middle, kinda like a horseshoe. YAWN.
Overall, I just am not having fun with it, and I'm beginning to regret my purchase. The campaign seems like it might have some promise, but frankly I'm not feeling very motivated to finish it. The multiplayer is pretty darn basic when you compare it to previous entries. Top it all off with the fact that they are pulling the classic "Season Pass/Paid DLC Packs" combo, and Gears of War 4 just doesn't feel worth the sixty bucks. Not when other games like Halo 5, an Xbox exclusive, or Overwatch, a third party game, have offered so much for completely scot-free. I'd wait for a price drop on this one, at best. I know the Halo 5 comparison is weird and might not be totally fair, like apples and oranges, but it's the one I'm giving you.
TL;DR: Gears 4 is basically just a Gears sequel with minor improvements to the gameplay and a lot of cutbacks overall to make it more like the first game, which makes Gears 4 an unimpressive game all around but worth your time if you're a fan of the series.