I've saved reviewing this game for a few years now, waiting until I finally had all the main DLC and whether or not I could up rate or down rate it.
Ultimately I've decided to recommend it HOWEVER, whilst the base game is certainly worth its non sale price, the DLC are not. As such I can only ever recommend buying the DLC when they're on sale, and even then it's a ridiculous price once it all adds up...
Also I will note that if you don't get the Extended Timeline mod, you're an idiot and missing out on roughly 1600 years of extra content :P

This was my first Paradox grand strategy game and I went into it knowing nothing, it is a very complicated game and took me many tries before I could play successfully and many months of me finding new features and mistakes I'd been making, don;t let that put you off and maybe use Youtube if you prefer not going into something blind. This is because once you've got the hang of it, this complexity is part of what makes this game so good.
That said, if super complex strategy games aren't you're thing at all, you may struggle to enjoy this game.

The game itself allows for huge replayability (pretty much infinite, especially with mods). This is because you can play as any nation that's ever existed in the time frame and each game will play out incredibly differently even if you don't change your play style or country one iota (which most people do change but I'm sure some don't).

Unlike the infamous diplomacy of Civilization games, or sometimes iffy diplomacy of Total War games (though the latter are getting better), the diplomacy in EU IV is well fleshed out and if you build relationships and alliances between countries, they're very likely to act how you'd expect, equally they don't follow you into war if there's nothing in it for them, they don't trust you, you haven't helped them enough or if it would rip their country apart, which is a nice realistic touch and makes the alliances feel more real and your wars will be more carefully prepared.
The way the economy, trade, wars and technology works are really nicely developed and fleshed out too!

One tip I will give you, regarding the UI, is that because the game is so complec everything is hidden away. Rather than exploring this straight away, would explore it on a 'I have a specific problem, how do I fix this', otherwise you will be swamped by choices!
The UI looks nice and is easy to use with practice, though.

My major gripe with this game (and CK II + HOI IV) are the ridiculous amounts of DLC and their pricing. Some of it should've been base game,m whilst others simply shouldn't be priced as high when you consider the content you get. The content and quality of the DLC themselves vary dramatically and I would suggest using online guides to decide which ones you want if, like me, you don't have tons of money to spare on this game at once (it's taken me nearly 3 years of slowly treating myself to DLC purchases and no doubt there are more to be released...).
I would say however by and large the DLC are worth getting if you can afford them, as they include features that enhance general play as well as specific cultures, playstyles, regions and countries.

TL;DR I would give it an 8/8.5 out of 10 on the basis that it is a really fun and great game with the possibility for hundreds (or if you have no life, thousands :P ) of hours of gameplay. It only loses points for the DLC practice that Paradox engage in for this game.
Certainly when it's on sale, it's a steal!

I've saved reviewing this game for a few years now, waiting until I finally had all the main DLC and whether or not I could up rate or down rate it. Ultimately I've decided to recommend it HOWEVER, whilst the base game is certainly worth its non sale price, the DLC are not. As such I can only ever recommend buying the DLC when they're on sale, and even then it's a ridiculous price once it all adds up... Also I will note that if you don't get the Extended Timeline mod, you're an idiot and missing out on roughly 1600 years of extra content :P This was my first Paradox grand strategy game and I went into it knowing nothing, it is a very complicated game and took me many tries before I could play successfully and many months of me finding new features and mistakes I'd been making, don;t let that put you off and maybe use Youtube if you prefer not going into something blind. This is because once you've got the hang of it, this complexity is part of what makes this game so good. That said, if super complex strategy games aren't you're thing at all, you may struggle to enjoy this game. The game itself allows for huge replayability (pretty much infinite, especially with mods). This is because you can play as any nation that's ever existed in the time frame and each game will play out incredibly differently even if you don't change your play style or country one iota (which most people do change but I'm sure some don't). Unlike the infamous diplomacy of Civilization games, or sometimes iffy diplomacy of Total War games (though the latter are getting better), the diplomacy in EU IV is well fleshed out and if you build relationships and alliances between countries, they're very likely to act how you'd expect, equally they don't follow you into war if there's nothing in it for them, they don't trust you, you haven't helped them enough or if it would rip their country apart, which is a nice realistic touch and makes the alliances feel more real and your wars will be more carefully prepared. The way the economy, trade, wars and technology works are really nicely developed and fleshed out too! One tip I will give you, regarding the UI, is that because the game is so complec everything is hidden away. Rather than exploring this straight away, would explore it on a 'I have a specific problem, how do I fix this', otherwise you will be swamped by choices! The UI looks nice and is easy to use with practice, though. My major gripe with this game (and CK II + HOI IV) are the ridiculous amounts of DLC and their pricing. Some of it should've been base game,m whilst others simply shouldn't be priced as high when you consider the content you get. The content and quality of the DLC themselves vary dramatically and I would suggest using online guides to decide which ones you want if, like me, you don't have tons of money to spare on this game at once (it's taken me nearly 3 years of slowly treating myself to DLC purchases and no doubt there are more to be released...). I would say however by and large the DLC are worth getting if you can afford them, as they include features that enhance general play as well as specific cultures, playstyles, regions and countries. TL;DR I would give it an 8/8.5 out of 10 on the basis that it is a really fun and great game with the possibility for hundreds (or if you have no life, thousands :P ) of hours of gameplay. It only loses points for the DLC practice that Paradox engage in for this game. Certainly when it's on sale, it's a steal!