Serious Sam: Siberian Mayhem is, more or less, Serious Sam 4 set in Russia.

It features the same gameplay mechanics, skill tree, weapon feel, and enemies (with 3 or 4 exceptions that you'll encounter only once each).

However, there are some improvements.

The graphics look okay now—no longer odd, unpolished, and incredibly buggy as they were in Serious Sam 4. No more textures randomly fading away or getting pixelated out of the blue.

The game is stable, with no more crashes or random frame drops.

And, unlike in some levels of Serious Sam 4, the objective marker points in the right direction this time.

Level design is really nice and genuinely feels like Eastern Europe, which I really appreciate.

Unfortunately (or fortunately, depending on one's point of view), the game is really short. At just under 5 hours, it feels more like a DLC than an actual standalone game. This didn’t really bother me, as I found Serious Sam 4 quite repetitive, boring, and a little too long for what it was, but it could have been 2-3 hours longer.

Overall, it is indeed an improvement over Serious Sam 4.

This was the usual boomer shooter I've come to expect, and although short in terms of episodes, it compensates for the length of each episode.

The inclusion of puzzles to open chests (don't recall if previous SS iterations had that) was a pleasant distraction. Interestingly, the inclusion of NPCs fighting alongside you was unexpected, since I was so accustomed to winging it out by myself.

One annoying thing about Serious Sam: Siberian Mayhem is that your vehicles can't pass through or demolish features like trees, which makes it annoying AF when trying to deal with enemies while driving. But I suppose it's to be expected, since nothing is ever easy in the series.

True to the franchise's form, the Serious difficulty level is as described. It was pleasurable enough to blast, maim and sometimes stab my way through waves and waves of enemies. Plus the brief bit on the last level where you have to sort of ice-skate through mobs was unexpectedly fun.

Now, for its drawbacks. Serious Sam: Siberian Mayhem's enemies, particularly the Kleer Skeletons, seem to have a noticeable problem with pathing, which is not too much of a hassle but is noticeable enough to speak of. But the most bizarre incident occurred on the fourth level. For me, it was when I went down using the large elevator in pursuit of the secondary objective, fighting the Cryomorph Gnaar Pair, and then making my way to the Russian partisans. I experienced unbelievably heavy lag, which made the game nigh-unplayable. Were it not for the fact that I ploughed through (and also because save for the pair, there were few enemies) I might have stopped playing altogether.

Since I can say I got my money's worth, I won't downrate Serious Sam: Siberian Mayhem. But I just wish Steam had the option of leaving neutral reviews instead of either positive or negative only. The aforementioned lag certainly put a dampener on things.