I was dared to play this game to completion, and I regret it immensely. While I successfully completed the game, I feel as though a part of me is now missing.
This game is soul crushingly boring and tedious, and while that is part of the Serious Sam style of game play, it entirely misses the point of what made the first two games fun.
This game makes you feel small, slow, and generally not very powerful. The enemies soak up huge amounts of damage even on lower difficulty levels and while the previous game had specific weapons to use against specific enemies, this one has several enemies that seem to have no weaknesses, and they enjoy throwing them at you in huge quantities(Footballers)
While there are sometimes big open areas and arenas in this game, you are often specifically confined to much smaller arenas than the previous game, and the designers just toss enemies one by one at you for 5-10 minutes. The developers even seem to realize that this is annoying because there are several voice callouts that Sam makes that emphasis that they are just tossing fodder at you in a padded fashion.
The game is split up into 7 distinct sections, the worst of them being the TV challenge series section and the ice world levels, where they introduce a resource mechanic where Sam will freeze to death, yes, Serious Sam will freeze to death, the man who can walk in lava. There are long auto scroller sections often with downtime or enemies on all sides, while confining you to extremely small areas and giving you very little in the way of dodging room. At one point there is a sewer level and the developers thought they were clever by saying all games had sewer levels and making it a maze, but it only calls out how much everyone hates these levels and it drags on far too long to be humorous.
While the developers added many new enemies to this game, they all behave as re-skins of existing enemies and don't add to the variety in play styles. Many of the enemies that people lamented from the previous games are back and more annoying than ever, almost as though they thought it would be a good idea to harass players of the existing games for having the audacity to question their design decisions. The flying enemies move around waaaay too much and too fast, and while you can usually lead them around, they tend to cluster directly above you where you can't easily aim, or stay way off in the distance where very few of the weapons they give you are effective.
They added turrets and vehicles to the game this time around, and it was a huge mistake. While the turrets are typically optional to use, the quantity and rate at which they throw enemies at you implies that they expect you to use them. Anchoring the player down is in stark contrast to the run around at the speed of light I loved in the previous game. The vehicles are typically overpowered and you just hold down mouse one and abuse the infinite ammo until it forces you to get back out of the vehicle. On rare occasions you get out to pull out the minigun and shoot down the flying enemies that you can't hit with the vehicle weapons.
The audio comes off as polished, but wears thin quickly. With as much as you hear the weapons sounds and musical tracks that don't fit with what you're doing, you grow tired of them, and I eventually turned off the music and turned down the sound effects to listen to something that wasn't going to put me into a coma.
The game while generally technically competent and feels polished, has a glaring technical flaw. For a game where almost every enemy runs straight at the player, the pathfinding in this game is horrendously broken if there are any obstacles. The enemies often spread out and run in the opposite direction of you, don't notice you at all, or get stuck behind objects that really should have been accounted for in the levels. This leads to parts of the game where you hunt around for several minutes trying to find the last few enemies that have become stuck in the level before the game lets you continue on. (You must kill all enemies to continue through the level.)
The pacing of the game is rather poor, and it takes away your weapons at the start of each of the 7 distinct sections and makes you run around collecting them, creating a saw wave difficulty curve, and ends up simply annoying more than interesting. They knew they didn't have enough content to make the game the 8.5 hours that it enforces on you, and it shows everywhere, leading to long drawn out sections that are neither harder, nor easier than the previous, just more of the same. If you finished the first three sections of the game, you've seen the rest. It's just another set piece behind the same tedious actions.
The boss design is typical Serious Sam, where you don't shoot the boss yourself, but play some gimmick that hurts the boss. Most bosses are invincible to player weapons(not technically but you could shoot them for an hours, run out of ammo and still not kill them), and they don't feel particularly rewarding to defeat. The first boss is possibly the most insulting boss I've ever seen in a game. If you take no action, the boss dies within 1-2 minutes, with no involvement. It's a "protect the AI while the AI kills the boss" battle, and I'm astonished they even put it in the game.
I'm giving the last level a special section because of how much I hated it. The last level is a one hour slog through 1200+ enemies while the game showers you in armor and health, and then throws an extremely tedious boss fight at you that will make you question your life, unless you exploit the terrible pathfinding on the AI fighters and hold down the fire button on the vehicle until the boss dies. In comparison with the typical level, it has nothing to offer that is new, just more of the same that you'd grown tired several sections back, and is more than 6 times as long as the typical level.
I cannot reccomend this game in any fashion. If you liked Serious Sam, pick up one of the others in the series, and avoid this one like the plague.