Server issue is actually unrelated to the event itself, so I don't think it should be brought up here.
Anyway.
Enjoyment: I do enjoy the event, I love seeing new maps and forms.
Quest Difficulty: This is for the main quest only, I didn't do the Cupid Bow quest since I feel "eh, not for me" regarding how it looks. The main quest is not too easy, but also not too hard and annoying. It's perfect.
Story/Lore: It's good. I'm particularly amused by the Nidoqueen-Jellicent part XD
Effort/Reward Ratio: For the main quest, I'd say it's fine. The Cupid Bow quest on the other hand, although I didn't do it, deserve a mention here - I don't think just one cosmetic item is a good enough reward after going back and forth traveling through an entire region to deliver all those letters. Maybe if there's something like a Master Ball as well for the reward, it would be more worth it. The Ayva's bag mini-quest, it's a fun little addition that's easy to do, but 1 gem is just too little, as easy as the quest is. Especially since it's a once per day quest. Should be 10 gems, in my opinion. Or instead of 1 gem, it should be 1 of those arceus plates, since they're really rare to get from digging.
Also, something to point out regarding spawn, the chance is not revealed again for whatever reason, but I feel like the chance for Valentine form is definitely not as high as 1/550 (Walross said Valentine chance is 1/550 in 2019), or even Halloween's 1/50, and even that I feel has been nerfed too, last year's Halloween event doesn't feel like there's 1/50 chance for Halloween form.
IMO, regardless of what's the event, special event form chance should have standardized "tiers" as well, at 1/200 for tier 1-3 spawn, 1/150 for tier 4-5 spawn, 1/100 for tier 6-7 spawn, and 1/50 for tier 8-9 spawn. The harder it is to encounter the Pokemon in the first place, the easier it becomes to encounter it as special event form, which I think makes it balanced. A tier 8 spawn shouldn't have the same 1/200 chance as tier 1 spawn for event form considering it's already super RNG (or super costly, when repel trick is involved) to encounter the tier 8 spawn in the first place, it should have gotten a higher event form chance to balance it.