A user system is a must, though should not necessarily be required to use the website.

The event creators should select some dates, and users should vote on which of these dates are good for them

That way, people that don't know the location or don't live nearby can get directions to the event

Users should be able to join gaming groups, and each gaming group should have a page with all that group's upcoming events. Perhaps users could even choose multiple events to join at once from a group's page.

I go to a game evening every week where everybody brings their own games. Support for this kind of event would be great. (Giving everybody the admin link would give too much control to everybody, allowing them to cancel the event etc)

User play History.
Tracking what games a user has participated in.
After a game-meet finishes, the "creator" of the meet must be able to add game-stats. Even if it's implemented very simple like assigning users for first place to last place, it can be very effective to have a general idea about:
- What games a users plays
- How good is he at any given game from meets he participated in
- Overall ranking based on this scoring, for info like "Who played most Catan and what is his experience"
- and many more :)

User attendance should be an indicator of how much can you count on a user showing up at a meet.
After a game finishes, the creator can mark users that MISSED the game-meeting.
This can show up in the user's profile as a percentage or badge.
Also, canceling an attendance subscription with less than 2 hours before the meeting is scheduled to take place, will mark the user as MISSED for the given meeting.

It would be great to create events that occur on a regular basis (weekly, bi-weekly, monthly, etc)

When i host an event i would like to receive notifications on comments and participants so i wouldn't have to keep looking at the page for new things

Each game has a limited amount of seats.
Based on extensions available to the meet-creator, he should be allowed to choose how many seats are available for playing.
The number of players expressing their desire join the game should not be limited to the number of available seats.
SO.
The meet-creator should be able to choose the users that will come to the meeting from the users that expressed their desire to play.

Google calendar, meetup, facebook, etc

A user should be tagged and ranked based on user behavior. The tags could be dynamic, but at the beginning of development it can be a simple set of tags like "fun to play with", "board geek", "competitive", "fair-play maniac".
Each tag should have a rating, and users should be able to anonymously set stars for each tag, this way defining that user's behavior. The rating data should not be available for users to see and should be kept anonymous. Only ratings should be displayed for a user profile.

This would be useful for both notification purpose and for having a crude way for other applications to get data from an event

We have more than a dozen games available, and I'd rather not have to search them all individually every month when I set up future events.

For example if the date, time, or location has changed, or to ask a question

This way if I want to include a link to Google Maps or an offsite seating chart or really anything, I have an "easy" way for users to view it.

To add RPGs as games to be played.