Honestly, there is nothing WRONG with this game per se, and I'm sure it's a nostalgia trip for many. Personally, there were so many games like this released at the time, and Shadow Warrior doesn't particularly stand out to me. But hey, it's free, so there's really no reason not to give it a spin.
Usually, when DLC are getting review bombed, it is the fans complaining about less than perfect AI, or the fact that Stellaris doesn't have tiles any more. Give it a rest, guys. Also, a lot of people just ignore diplomacy and play min-maxed purifiers. As someone who does use the features Federations provides, I can say that it does improve the single player experience. The new origins alone make this DLC worth getting in my opinion.
I can't say I've regretted any Stellaris DLC I've bought, but Megacorp comes the closest to that. At its core, Megacorps do add a bit extra to a Stellaris run, and a can make pacifist play-throughs more fun. Criminal syndicates and cults are especially neat. However, the rest of the features are a wash. The slave market (which should have never been locked behind DLC) doesn't work half the time, caravaneers are horribly annoying, and xeno-compatibility is just a dumb gimmick. It's hard to say that I've gotten my money's worth if I usually end up turning most Megacorps features off. To add insult to injury, installing Megacorps permanently gets rid of Nomads. In short, Megacorps is usually considered the worst Stellaris expansion for good reason.
A lot of players of this game either only play competitively, or just like to min-max the same build ad nauseum and don't care about anything else. As for me, I like story and world-building. Distant Stars does add a lot to the replayability of Stellaris, but that is only worth it if you REALLY like Stellaris.
Beyond Utopia and Leviathans, which DLC you buy for this game really depend on what you want to get out of a game of Stellaris. Apocalypse adds a bunch of fun late-game technologies that are satisfying when you finally get them. I personally enjoy Marauders quite a bit as well. But DLC is still DLC at the end of the day.
You can definitely make a case for Paradox putting more time and care into Stellaris DLCs early on. Leviathans goes a long way toward making the galaxy feel more alive. It is also a good DLC for beginners that struggle to obtain some of the later-game technologies. Not quite as essential as utopia, but do pick it up.
The fact that synthetic dawn is considered a story pack and not a species pack is not a misnomer: you get a lot more with this than a couple of new hats. Robots play significantly different, and can be good for a beginner player struggling in the base game. Even if you don't play as robots, having robots in the game can definitely spice things up, especially where certain events or crises are concerned. It's more bang for your buck than plantoids, anyway.
I stumbled upon this game after a disastrous run of Star Control 2. Stellaris scratches that itch and more. Granted, it's not a better game. In a way it can be better thought of as a sandbox than a strategy game: build yourself a little world, and play in it. That's fine for me, however a bit more emphasis on overarching scenario plots and the potential for character development would be appreciate. You can safely ignore the review bombing this game gets every time a DLC is released, because the fanbase are completely out of their minds. Hopefully this game distracts them somewhat from strangling cats and putting bananas in car tailpipes, or whatever it is that they normally do in their free time.
For a long time, SS5 Special was something of a holy grail in the series, an arcade-only revamp of the underwhelming Samurai Shodown 5 that basically perfected the formula of the series up to that point. I have had the pleasure of playing it in arcades, but I also appreciate a competent home port, which this is. Being a dream match game, you won't get much in the way of bells and whistles, however. Still, for the price you really can't complain.