This game is absolutely incredible, but only if you aren't discouraged by failure, are willing to engage with the game to learn the quirks of the plants and zombies, and enjoy high difficulty.

With that disclaimer out of the way... I have played a lot of Eclise! I beat all the levels in "Eclise Beta" several years ago, and then later replayed the entire game after it had a soft reboot and was ported to a different version of the vanilla PvZ2 APK as "Eclise Alpha" (I don't know why the beta came before the alpha lol). I have seen a lot of backlash to the alpha version for changing the optimal playstyle and tweaking other things, but I'm here to tell you that both versions are excellent! The beta is easier as sunflowers are much stronger in that version, but the alpha version also has an optional easy-mode version that you can play, where zombies have less HP, so I would honestly just recommend playing the alpha since it has more content, a more consistent difficulty curve in the campaign, and is better balanced.

Now onto what I think actually makes Eclise so great! I think that vanilla PvZ has amazing ideas and does not explore them in meaningful ways. It is incredibly easy to just absolutely steamroll every level with nothing but the most basic of plants. The levels in the original game are also extremely short, making high cost and long recharge plants less viable as well as making the game even easier. Eclise has much longer levels with waves of zombies that get much more dense as the level progresses. This makes the game much more interesting as it leaves you with much more impactful decisions to make. You will have to decide how much room you save for sunflowers, what plants you will want as early level (cheap and weak) and late level (strong and expensive) damage options, what archetype of plants would be effective in a given level (torchwood + pea, ice + AoE, shadow plants, etc), and much more.

In addition to having over 100 plants to choose from in a fully completed save file, every plant has 3 different unlockable "tiers" that you can change to customize their role a little bit. None of the tiers are inherently better than others (in theory at least). For example, T1 peashooter costs 100 sun and does 40 damage per pea, but the T2 peashooter costs about twice as much and does about twice as much damage. This significantly increases the versatility of all plants and allows for more nuanced deliberation for your seed deck. It is also incredibly satisfying to unlock new tiers for your plants, giving you more options to allow for different strategies and increased skill expression.

One of the only negative things I can say about this game is that sometimes you just aren't prepared for ambushes until its too late. The crux of a level might be that there is a huge zombie ambush halfway through the level, and the game won't communicate this with you until the ambush is actually happening. This can lead to some frustrating "well how was I supposed to know that was going to happen?!" moments that you wont know about and likely wont be prepared for until its too late. I personally rarely found this to be more than a minor annoyance, as it rarely happens and it can feel good to go through the level a second time with significantly better performance since you can select more appropriate seeds after getting the chance to scout the level. This is often a necessary evil though, as experimentation in overcoming great obstacles is what makes the most challenging levels so rewarding. Another small gripe I have is that I found some level gimmicks to not be fun, but there are so many 1 off gimmick levels that encourage different styles of play that it seems inevitable there I wouldn't vibe with all of them, and they are an overall positive addition to change up gameplay.

Eclise gets a lot of unfair criticism for having consistently bad design, excessive difficulty, and "zombie spam". I can acquiesce that the optional secret levels get incredibly difficult but virtually no levels in the game are poorly designed, and I think the extreme difficulty in the optional levels are great optional skill checkpoints for the player to display mastery of different mechanics. Eclise does an excellent job at setting up the player for success by teaching them relevant strategies and it then expects you to engage with it by utilizing what it has taught you later with greater stakes. I think most players who have complained about the game being poorly designed likely played Eclise expecting to be able to play it with little engagement, like the vanilla games, and then had a skill issue.

TLDR; Eclise takes everything that worked in the original Plants vs Zombies games, changes everything that didn't, and adds heaps of its own ideas to the mix to create the ultimate Plants vs Zombies experience. I urge anyone who likes strategy games or PvZ to try this mod!