addicting and visceral combat.
I guess the only new mechanic gears had was active reload and a chainsaw gun.
I'm sure I played a game with an active reload type concept before. Possibly tapping reload faster to load shotgun shells faster, although I can't remember any particular game so ignore.
What content was gears lacking?
Anything but on-rails shooting? Shooters used to be a blend of various styles and had a fair bit of depth often overlooked by the uninitiated. See Duke Nukem 3D: platforming, puzzles, exploration, ammo/health/inventory conservation, interaction with the environment, level design that offered some degree of freedom and in itself was a game to be beaten (environmental hazards, traps, crafty enemy placement, navigation/orienteering etc). That in addition to just as much shooting as Gears across the course of the campaign, and it was longer in game time. Hell you'd even find a jetpack on some levels and could fly around for a short period of time, making some obstacles easier if you used it wisely, or flying up to a vantage point to escape a horde of enemies or do some sniping.
Shooters being way more than just shooting was standard design once upon a time, on both PC and consoles, third person and first. Things changed around the early 2000s, but even plenty TPS and FPS of that era still had a lot to offer in comparison to the next era of bland brainless simplicity spearheaded by Gears and the like.
Even Half-Life, a game said by some to be early railroading and decline, still was about platforming, puzzles, navigation of the environment, strategic freedom (do I run behind cover? Jump to a vantage point? Pull out my rocket launcher and potentially waste its limited ammo? etc) and so on just as much as it was shooting shit.
I still enjoy linear tightly controlled simplistic games, such as racing games or 2D platformers, but GoW isn't even a good simple game. It's just rubbish.
More things to criticize about GoW: bland monotonous art style, cover shooting reducing depth and skill level involved in shooting, instantaneous regen health removing tension, strategy and difficulty (although regen health is somewhat suitable for multiplayer, imo), the game was generally easy...there's absolutely nothing I have to praise about its game design as an entry to the shooter genres. It beggars belief that the incredible accomplishments of EPIC's engine programmers was wasted on such shit receding game design.
Before cover shooters the player would walk up to cover and press "crouch", if the time called for it. This was only a very small component of the game experience, not the whole thing revolving entirely around it.