when the player attacks a monster, he has to wait 5 sec before attacking again for example) in an attempt to increase the time spent on one page, and it improved things a bit.

So in order to increase earnings, you have to lower the quality of the product! Then, what happens is that people click the ads because they are sick of your site and want to leave.

Sounds like maybe you have the wrong business model. I'm thinking of comparisons to Runescape, for example, where there is a free area that you can play, but if you want to progress you have to pay. That would a different way to monetize.

If you're going to advertise, maybe you need to look for a couple of choice, relevant affiliate programs, rather than taking your chances with adsense.

Unfortunately there are no "tricks" as such, you just need to find the right niche. In your case you already know that your visitors land on your site with only one objective in mind. Many of your visitors are also likely to be repeat visitors which will compound the problem.

3 sec is sensible since it's about what it takes to read the combat report - from the support forum no-one has complained yet :)

But point taken, this is not a good approach to improve the eCPM.

I intend to indeed provide a premium account to players when the website will have more features and players (I've put the site online only 3 weeks ago) but until then I'd like to try and improve the adsense approach.

I would think you would have a problem with the ads that your visitors are seeing too. What kinds of ads do you get? How does AdSense figure out what ads to serve? And are they ads likely to interest your visitors?

Banner ads paid by impression might be a better choice.

eCPM is rubbish

That's putting it mildly!

There are other things I can say about the low eCPM, but it's not appropriate for this forum.

Well,

I used to earn 50K monthly from adsense from 5 millions daily impressions.

Nowadays, I can barely hit 4K.

How many unique visitors are there, that's the number that really matters. Everyone above is right though, this niche will not make a lot of money.

1- I doubt the ads are well targeted, and they may never be
2- people aren't looking for information
3- people don't want to leave the page of a game they're playing
4- high page views from users playing the game will surely artificially decrease your eCPM
5- etc

I could go on and on about how Adsense is not an appropriate match for your site, and the figures prove it. Try CPM banners instead, or affiliate products. Don't try to force a square shape inside a circle hole.

use a cpm network adsense wont work for your site

You wrote, "10,000 page views.". But how many uniques it that?

10,000 page views in your niche might be worth little because few players make lots of page views.