Absolution was my very first game on Steam, I was hyped for it and was happy to put in a solid 150 hours to explore and complete the challenges. Yet today, it is considered the "black sheep" of the franchise.
To understand why it is so, we need to go back to origins of Hitman. First 3 games - Codename 47, Silent Assassin and Contracts - for the most part were shooters with a twist of being able to use stealth, as well as social stealth through disguises. Going in guns blazing was a very viable way to play those games, and they really supported it. For example, Contracts let you wear SWAT uniform on three separate levels, increasing your resistance to taking damage. It also routinely featured weapons like M60 machine gun and even a minigun. However, the common criticism for games of that era was that sneaking around was pretty pointless and in a way invalidated by gunplay.
Then came Blood Money. Blood Money is widely considered the best Hitman game for essentially doing two things. First, it made the levels bigger and turned them into those assassination sandboxes to experiment with. Second, it really improved on stealth, adding many things we can't really imagine Hitman without today - all those boxes to hide bodies in, accident kills, et cetera. Blood Money still maintained a healthy balance between stealth and gunplay - this was achieved through allowing you to customize your weapons, including things like drum mags and magnum ammo, able to pierce through doors. Another achievement of Blood Money is how it tried to balance the two approaches by introducing realistic penalties, for example if you went in guns blazing in the first level, you would be easily recognized in the second, unless you paid to change your identity and stuff.
Absolution feels and plays like one of the Hitman movies. Its main crime in the eyes of fans is trading away assassination sandboxes for fairly small, linear, corridor-y levels with the recurrent theme of "make it from point A to B". Its biggest open level with multiple assassination methods - King of Chinatown - is not only a one-off but also can't hold a candle even to the smallest map of the latest Hitman trilogy. That being said, Absolution really went the "less is more" approach. There are realistic consequences for going in guns blazing. For example, if you kill cops in Chinatown - SWAT will arrive to deal with you. You can take hostages to use as human shields. You can switch to using one or two iconic Silverballer pistols on the fly, and put suppressors on them with a press of a button. And let's not forget point shooting - a very cinematic mechanics to headshot multiple enemies at once.
The trilogy that started in 2016 is simultaneously the best and the worst Hitman in the franchise. The best because it doubled down on what Blood Money did and made assassination sandboxes bigger than ever before - it's very fun to explore and experiment with them. And the worst because it changed the genre of the game to a puzzle. Basically, it addressed the criticism about stealth being pointless in the most radical way possible - by making 47 weak to damage, doing away with any combat-oriented mechanics and even the ability to use pistols in both hands. So while assault rifles and all still exist in that game, unlike the previous games they are not fun to use anymore.
So why don't I recommend Absolution for anyone starting out with the franchise? For one, it's not representative of the traditional Hitman game structure - that divided into levels, each of which has you assassinating a target. Secondly, if you start with Absolution you might grow to perceive Hitman as an action game where combat is fun and supported in terms of mechanics. And if you play the modern trilogy afterwards expecting the same, you might be in for a disappointment.