Based on the last clue, I'd guess it's called Slice and Dice?

40
- If you go against one of the main conventions of the game in the first level, you’ll be rewarded.
- Your foe is now your friend… or is he?
- Your sister certainly doesn’t believe him

39
- A launch title for the first system it released on, it was sometimes criticised for having dark visuals that made it difficult to play on original hardware (subsequent hardware revisions remedied this issue). This is supposedly the reason the next game had brighter graphics.
- There are four unlockable modes, each of which give your character a boost on one specific attribute at the expense of others - magic, strength, subweapons, and luck.
- In some regions, this game shared the same name as the very first game in this series (other regions added a subtitle). Funnily enough, that first game was later released on the same system, as one of a number of classic games that were reissued.

38 - Doom II
- Introduces a few new enemies to the series, but only one new weapon. And even then, it’s more an upgrade to an existing weapon, effectively doubling its power.
- One of these new enemies is a vile creature that can resurrect fallen foes.

37
- What once got you access to the garden, now allows you to collect a powerful weapon.

Current list - https://gamrconnect.vgchartz.com/thread/247804/the-official-thread-the-14th-annual-greatest-games-event-post-only-once/4/#3

Indeed it is.

#38: Doom II. Didn't get it with the super shotgun, but the Arch-Vile is a giveaway.

Yep, Doom II it is. The Arch-Vile has caused me all sorts of issues over the years.

43 - Deathloop

Yes. Last year my hints for the game were too difficult, this time it's too easy. I need to find a middle-ground.

OK, I drop my table for the guessing game here again, to keep the post in the official thread more focused on the games.

The most current hints are here.

The final results so are:

Two games have been guessed, three to go. Here's extra hints for these;

#40: Probably the coolest special edition I own is the one for this game, it comes with a wooden miniature of an Onager that you could build yourself.
Hint 2: At launch the game was criticised pretty heavily by players however. With a slew of updates adding things like a family tree and overhauled politics, much of this criticism has subsided.
#37: Technically just a sprite swap of another strategy game, and considering the franchise this is part of, shouldn't they have done more?
Hint 2: The basis for this game is a famous rts from an otherwise completely unrelated franchise and developer, but my game's gameplay is basically exactly the same, down to the building types and technology (in the sense of advancements and upgrades for the purpose of the gameplay).
#36: A handheld entry in the series which unlike its console brother actually is a numbered sequel.
Hint 2: These two games were released pretty much simultaneously.

38. Super Mario Sunshine
The addition of Fludd turned a lot of people off on this title and I can understand why. Although, it's used well in some cases, stopping to spray and managing your water levels slows down gameplay compared to Super Mario 64 where you're almost always in motion. I didn't mind the change up, but what really sold these game to me was its creativity, especially since it's all constrained to one island. Unlike the paintings of the previous game which sent you anywhere and everywhere from desert to docks, iceberg to interior of a clock, every place in Sunshine was part of Delfino island and you could even see other levels in the distance. And yet despite being all part of one island each place had a very distinct personality and feel to it, along with all sorts of crazy troubles to deal with. It really made the game feel like one continuous story rather than an arbitrary number of levels needed to unlock a door.

New Super Mario Bros 2. The release date was relatively close to NSMBU so I'm calling that simultaneous enough for my guess.