Was it successful? Well, this is subjectivity. As for me, the answer is 80% "yes". I will try to make a justification to my answer.

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One of the biggest pros in this game is a color design along with procedural generated levels. It's colorful, it's beautiful, it baits you to lose focus from your character and just look around. Each shard ("world") feels different. Here you have a default green landscape, here - a desert, here - something full of pink color etc.
Overall, visuals of the game is perfect.

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Haste is a high-speed running game, as developer says, and it's totally true. You can feel the character's speed, It's easy to feel any changes in the speed and after getting used you can control landing pretty well.
In addition, the player has some helpful features like hoverboard to control landings better what leads to less speed losses.

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I know it's kinda useless point considering its requirements, but just if someone wondered, the optimization is good. It's not perfect or ideal, It's just good.

This is a tricky question. I can definitely say the game has a huge potential to have a good roguelike repetitiveness, but... it feels like it won't be true.
The main thing which baits players to play more and more runs is a huge number of different items with unique effects which can often be a game-changer. The second thing is characters with different skins/outfits and more important - different abilities.
What do we have in Haste? Uhm... almost nothing?

Originally posted by author:

Just a quick remark: Right now I'm on the shard 3 (3d world), so I don't have the highest rarity items and obviously haven't unlocked a lot

Talking about items, most of them are created with formula "On close call / on use / on entry + gain/restore + *number* + hp/energy/boost" for trigger/active items or "plus + *number* + hp/energy/boost" for passive items. Hear me out, it's not that bad for items with poor rarity, but I felt like i don't have enough options to "taste" high-rarity items. All i can do to get them is to grind special points (more runs = more points) to upgrade items rarity.
The problem which bothers me is that i've already encountered some items with higher rarity with the same effect but longer duration.
If I understood correctly, we won't be able to play any others characters, but we will get some abilities. Right now i'm on the way to get a grappling hook from one of the NPCs. Probably, we will have even more abilities... at least 4 of them according to dev's words.
Tho, I have to admit that getting abilities by grinding that special points is kinda awkward. Imo, its way more interesting to do a special quest or to meet some conditions to get a new ability.
Anyways, not having other characters leads to a problem of inability to change the outfit or skin of our main character. I'm sure there will be a lot of custom modded skins, but it would be great to have such feature done by devs.

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Haste is not pretending to be a game where you are going to spend hundreds of hours unless you are really into its gameplay.
This game is about taking a breath of fresh air if you are used to play roguelike games. It's good, it has unique gameplay. It's interesting to grind for maybe 10-20 hours, but it can be boring when u've played too much.
Today is just a day it released, so we can have our hopes that devs will gather feedback and fix poor repetitiveness. Tho, right now it is what it is.
As for me, 8/10, because i love high-speed gameplay.