Hi!
I just would like to let you know that for being in an early stage, this simulator is looking to have a lot of potential! However, there are a few things that I would like to suggest to help improve the simulator as a whole. I feel some of these have probably already been mentioned, but I really don't wanna sift through 12 pages of posts just in case my suggestion was already made so sorry in advanced for repeat suggestions.
#1. Now I know for a FACT this has been suggested, but I'm gonna suggest anyways because its important - the ladder needs SERIOUS fixing. The points system makes absolutely no sense and I keep running into very low points players even when my score is somewhat higher (1750-1800 running into 600-900 points players?)
#2. A real means of saving replays/logs. It's been so frustrating to accidentally exit out of a battle to never be able to see that replay ever again. I battled a friend of mine and we had a really good battle he wanted to record for his youtube channel only to realize afterward that if you exit out of the battle window, your replay is lost forever. Please fix this. lol
#3. Tournaments and Friends lists. One thing i really liked about PO was that people could host tournaments and such. The fact that you have to go through some external program to host a tournament seems silly to me. Also, I think something that would add a lot to Pokemon Showdown is friends lists. Many other online gaming clients these days have a means to log friends and people you meet online to communicate, challenge, talk to and see if they are online. Why don't we move pokemon simulators in this direction?
#4 Small little help section for newer players. Now this last one is a little nitpicky and not even that necessary, but i've noticed a larger number of novice players on this server than the Smogon PO server back in the day and I think maybe having just a few links to guide players in the right direction (maybe a link to the Smogon analysis page, a short brief description of EVs or IVs, etc.) would help marginally increase the skill level of players. Maybe call it a "Is this your first time here? If so click here" and give the rules of the simulator and a small little guide toward getting started battling.
Anyways, good luck and I hope that you take my suggestions with some consideration!