It's... alright. Like it's not a hard no by any means, it's a fun enough game I guess, but the issue is just that there are vastly better games that have far more content and more interesting progression options, and which are cheaper or just free. I'll go into more detail in a moment, but want to emphasize this a bit first.
In and of itself? If it was only being held to its own personal standards? It's a bit overpriced for maybe ~4 hours of content to reach the 15th warp. With the -45% off sale that I got it for about $5CAD, I don't feel like it was a waste of money or anything, but it doesn't feel like I could really recommend it at full price.
So... the game itself is fairly straightforward - you have a reactor, you add various particle types, some are used as fuel, some burn the fuel, some modify how the fuel or burning works. It's a kinda clunky physics simulation and I kept hoping they'd increase the radius of the fuel burning part, but it never really does work out that way and honestly is kinda clunky, even with other options added later on to make burning fuel easier.
That's not a huge deal, but nothing in Feed the Reactor is really a huge dealbreaker in general, it's just always a bit disappointing. Things like how every single upgrade is additive instead of multiplicative. Yeah, X2 is nice of a bonus! ...X3... X4... X5... x50... you're getting diminishing returns as you keep putting more and more points into it. The solution to this is to get different things working together, but it always follows the same pattern of becoming less and less valuable so you just have to add some new element to make up for things becoming very high in cost but minimal in increased effectiveness.
That's pretty much what I found with the whole game, was that the 'progression' part of the game never really felt much like I was making any real progress. Upgrades kind of take a while to build up to and then don't really do much. This is for balance reasons, to keep the numbers tightly controlled so that the designer knows pretty accurately how powerful you are at any given moment during the game, but it's rather disatisfying in a lot of ways as well. Part of the progression/idle genre's big draw is the silly high numbers you can reach. This one gets up to about the sextillion range, but it never really feels like you've come all that far from the start because all the increases are very minimal each time and peter out in effectiveness almost immediately.
There are a lot of points in the game as well where new options aren't really that helpful when you first get them, or things where you clearly are supposed to have access to a feature long before you actually get it unlocked. Given the extremely linear gameplay with minimal choices available, and how tightly balanced a lot of the design is (to the point of being detrimental), this feels especially odd to have things substantially delayed by sometimes half an hour or longer between when you get things that benefit the upgrade and when you actually get the upgrade itself to use those benefits.
Either way, it's not a bad game by any means! If you like idle progression games, it's perfectly playable, it's just... it's competing with things like orb of creation, kiwi clicker and so many others that are just flat out better which are cheaper or free.
I won't say don't get Feed the Reactor ever, I'd just say look through the list of other games out there first. This is probably somewhere in the middle range, maybe 5/10 or 6/10 compared to others in the genre, a little above average maybe, but not by much. When you've gone through the top end and are still looking for more to do, then possibly look into Feed the Reactor, but it's definitely not something I could recommend as your first game in the genre, nor even the second, third, or even tenth.
I think it's still worth playing eventually, but it's really not anywhere remotely near the top of the list. You can definitely do better, but if you've exhausted the better options, it's not a bad one to try out after a while, but I can't really recommend it when there are vastly better options to recommend first.
