I also just came back from ElSol and will (mostly) agree with the above comment.
The attendance seemed to me to be ~1000 people (accounting for different rooms and the fact that the early/late dancing crowds don't overlap much, if at all).
There was always more than enough space to dance in the bachata room. The salsa room was more packed, but mostly had enough dance space. Cuban room also seemed to have enough space to dance the 2 times I went to see what it looked like. I didn't bother attending the other 2 rooms or the day socials.
Follower salsa dancing level was very good, I was pleasantly surprised. I had at least 20 dances I would classify as "great" and only 2 that were borderline bad (but I could call them mediocre if I squint a little).
Bachata follower level was not good.
The festival had slightly more leads that followers but by little (maybe something like 11:10 ratio). In the bachata room there were almost always twice+ as many free men than women. The salsa room was more balanced. Due to the higher number of people there, there was always a free follower to dance with.
Attended a total of 6 workshops, standard festival stuff. Johnny Vazques' sunday partnerwork workshop was too crowded.
The hotel was overall meh - decent breakfast, the room was basically the size of a rich man's closet than a regular bedroom, but at least it's functional for an airport hotel. (It's more interesting that the same room is also sold as a standard double room - I have no idea how that works; it's obviously only for couples as one bed, but I would not be caught dead forcing a girlfriend sharing that room). The main problem with the hotel is that it's overpriced - 340 euro for 3 nights + breakfast. This is Warsaw, not Copenhagen.
I didn't attend the live concert on Saturday (the band were some cubans who apparently live in Poland - so were probably hired for convenience; no idea if they are good or not) but made the mistake of going to the Saturday shows. The MC was annoying as hell and I really did not need to hear about the organizer's 28-year old boyfriend.
Overall, I'd rate it as a positive experience but I'm not sure it's really worth the money.