Ok, I decided to check on reviews on YmirRO here, and so far, I haven't seen much reviewing discussion. I have seen things more along the lines of trolling and flame wars. Either that or I haven't read far enough. So I'm gonna put my opinion here. And no, I'm not being biased.
Where to start?
Well the community is small I have to admit. When I first joined, the server size was alright (even though it was my first time playing with uni friends). Normal days, we had about 40 people. WoE nights about 81. WoE was fun for me then, and then the famous server and forum crash for a month came in and killed it. When it reopened, we had very little people come back. From then, the server started growing again, but slowly. Today, we had about 35 people online (minus-ing the merchants that are afk or whatever) for WoE. So the server size isn't big and you will probably get to know half the players there well. But don't worry, most of the players there are nice and will help you out if you have a problem.
WoE times are usually on weekends, so most people can make it. A second WoE time might be implemented soon. There hasn't been much castle rotation, but no complaints on that as of yet.
The GMs there are fairly active. I don't know about GMs on other servers, but Ymir has been doing a great job holding up the server and trying to make it grow into something great. Odin and Loki have also been great staff. If you have a problem, post a reply on the forum or in-game, and they will get it fixed ASAP. But I haven't seen them on often, probably because they all busy with uni or work, but they do get the job done. They were on often during school holidays though. Are they corrupt or biased? Well, I don't think they are. Ymir tends to be over-protective, but I guess I would too if I wanted to keep a server running that's hanging in there and keep things as clean as possible. Bots don't stay on long, so you can be sure its bot-free. The GM team, with the help of players, catches and ban them pretty fast.
Lag, well there's very little. You will probably feel some lag maybe once every 2 or 3 days. But I don't find any on my end. There are sometimes disconnections (very rare), but they have stopped and haven't re-occured for about a month.
Events happen fairly often. We get like 5 events or more every week (correct me if I'm wrong). So far the events are usually "take out the double-HP MVP" or "clear the huge mob", but there might be some changes (I hope).
There are NPC-warpers, healers, a skill resetter, PVP rooms inplemented. I'm pretty sure those are standard now for low rate and mid rate servers, but its good to know. The healers require money for them to heal you. 10z for HP heal, 1k zeny for HP and SP and free blessing and Inc. agi buff. The healers aren't helpful at the start IMO becoz you have no money to recover SP. So you sometimes have to sit for 3 mins for a full SP heal, but Ymir is fixing that. Resetter is very helpful and costs 5k for each type of reset. The PVP rooms are good places for your general duels and guild wars. Generally, I like having them there.
Rates are 10/10/10. I find 10/10 exp kinda slow, but that's prolly just me. x10 drops rates means you still got to put in the effort to get your gears, so that's pretty balanced. Although I miss the x30 quest exp the server used to have, because Ymir said there are repeat-able exp quests but I don't see any.
I heard about some servers having donation items that are godly and Card Selling NPCs and whatnot. YmirRO doesn't have these. Ymir loves things to be balanced and you should work for your items, gears and imbaness. You can donate if you wish and get OPBs (I think).
WoE these days are now action packed and will cause your computer to rumble and lag (maybe not). There will be destruction of every type in every corner of the room. WoE 2 has also been implemented and is almost as crazy as our classic WoE. So far, we have 3 guilds going head to head and smashing each others brains out. Its pretty awesome.
The economy is now much better than it was before. The items are now more reasonably priced and bargaining never felt so good. With the population much higher, more farming from all means more goods on the market.
Since I ain't an experienced RO player, I can't really give it an accurate score. But I would give it 8/10.
RMS Server Info on YmirRO:
http://ratemyserver.net/index.php?page=detailedlistserver&serid=4084&itv=6&url_sname=Ymir-ROSummary1. Friendly server
2. Helpful and fairly active GMs
3. Bot-free
4. More or less lag-free
5. Events twice a week. More during holidays
6. Free NPC warpers, healers, skill and stat resetters, PVP rooms available
7. 10/10/10 rates
8. No donation items and NPC MVP card sellers
9. Pretty hectic WoE
10. An alright economy
11. Classic WoE and WoE 2
12. WoE times on weekends