This is less of a review and more of a preview of what you can expect from this game. I know that steam says I barely played EL - that's because I've been playtesting this game for several months before release. As such, I'm also inherently biased so take that into account.
Why should you buy this game? The short answer is - if you have any doubts, don't buy it. Wait for the full release and then do your research and see if it's the kind of game that you will enjoy :)
Personally though, I think that EL stands strong among other 4X games. It feels fresh and unique in many areas where 4X were starting to get stale. There's a lot to talk about so I'll just go over some of the bigger features:
Firstly, the city management aspect. Like in most 4Xs once you make a city you can grow it, make improvements, train troops, gather food, industry, science, dust/gold and influence (FIDSI in short). But population works differently - you assign your workers (you population) to specific areas like food generation or influence generation. The amount of population working on that is multiplied by various bonuses (but it's at least *3) and then other various other bonuses are also added to the amount of FIDSI you can generate. This gives you a lot of control over what your city does (more so then in civ where you're much more dependent on the tiles around your city).
Secondly, empire management. Every 20 turns you (and all other players) choose your "empire plan" which will define how you play for the next 20 turns. You need influence to invest into your empire plan - the more influence you invest, the better. You also have more options in empire plan as you enter new eras.
Another use for influence is in diplomacy - all diplomatic actions (closing borders, declaring war, etc) require some influence. You can also spend influence to improve your influence with AIs. Right now however, this aspect of the game only has basic functionality because there's no multi (yet) and the AI is fairly dumb (for now).
Additionally, the tech is non-linear, meaning that you have free control over which tech you want to go for next. There are no prerequisites to anything. However, you have to choose what you research wisely as technology gets progressively more expensive. The only limitation are the eras. Basically, in order to unlock tech from next era, you need at least 10 tech from previous era.
Thirdly, army management. There are 5 main unit types in the game: infantry, ranged units, support units, cavalry and flying units. Each faction has access to 3 unit templates (+the settlers) which you can then customize to decent extend. For example, you can equip your infantry with weapons that will help you fight cavalry - which normally is a good counter to infantry.
Because each race can only use 3 basic templates (in as many versions as they want of course, I'm just talking about the infantry/support/etc kind of templates), you also have to rely on assimilating minor factions into your empire. Minor factions will grant you an empire bonus and give access to their unique unit templates. This allows you to make up for the fact that you don't natively have access to certain unit type. For example, the Wild Walkers faction has no access to flyers so they can assimilate Khazanji minor faction to gain access to Demons - a new flying unit template. There are of course limitations to how many races you can assimilate.
Fourthly, the battles. They're quite unique since they're played on world map (like in civ) but are little skirmishes by themselves (like in AoW3 but you have less control). Each battle starts with a deployment phase and planning phase (during which you give your units orders). Then, the battle kicks in and you watch how your units duke it out. After a while you get the opportunity to change your orders around if you so choose. You also have to remember that there's elevation in this game - attacking from high ground will give you a decisive advantage while using cliffs can lead to some Hot Gates scenarios. The battles still have ways to go, true, but they're quite enjoyable already, even in alpha state.
Lastly, the world. Auriga (the planet you play on) looks gorgeous and I wouldn't hesitate saying that it's one of the best looking 4X games (if not the best). Aside from great visuals, there are numerous things to discover on Auriga - there are many anomalies (special tiles that are usually very good), ruins to explore (they are persistent btw), minor faciton villages, and a huge amount of various biomes. Plus the standard - resource deposits and so on.
Also, let's not forget about quests. Each faction has a storyline expressed via a quest system. Every player is given a set of quests that they can complete for rewards (completing all of them will win you the game but that's not implemented yet). Aside from these main quests, you can also gain various side quests from minor factions, ruins and so on. The quests are quite interesting and make the game feel more alive, they also let you discover the lore of the game.
In general, I do recommend this game but encourage you to do some more research first. Especially if you plan buying it in its alpha state.
Also, this review is mostly a quote from a wall of text I wrote on the forums once. Just FYI ;)