[Necroterra]

This is one of those things where the dream version is absolutely amazing, but reality tends to get in the way. I hope this works out, and have a couple thoughts off the top of my head. I will use some references to games, as that is what this is.

• How are you funding this? It will only get more expensive to maintain and grow this as it goes forward, and with good design/everything else, you could easily get more traffic / demand than you can pay for.
• You probably will want to monetize somehow, but in a way that doesn't drive away your playerbase. This is very hard to, and bad pay-models have killed many games and projects. Cosmetics are pretty safe: "$20 gets you a golden robot" is less alienating than "$20 wins you ever match"
• How many people do you have onboard? Do you have advertising and PR? Do you anyone with game design experience?
• Consider the comparative complexities of MOBA type games and FIRST games. Dota 2 has >140 items, >110 heroes, different jungle camps, scaling creeps, roshan, runes, towers, barracks, buyback, catch-up mechanics, a meta, hundreds of skills, multiple hero roles... an FRC game tends to have 1-3 game pieces and 1-5 scoring mechanics, but can get away with it due to the innovation in actually building the robots. Obviously your game will fall somewhere in the middle, but mechanics such as currency, upgrades, dynamic environments, non-player entities, and so on will up the ante in terms of strategy and player retention. No one would want to play remote Recycle Rush, for example.
• Keep in mind various levels of play. Some people will want to hop on, drive a robot into some walls. Others might want to chat with teammates and try to win. Others still might want to form a team and compete in tournaments. Social features are what make multiplayer games successful; for proof, see WoW, Dota, League.
• Larger robots could be controlled by multiple people - either "Star Trek" style, where each person does a different task, or "crowdsource" style, where everyone's actions get averaged out. (The crowdsourced one will work better for robots that work over long periods of time, so that people can cooperate.
• Quality over quantity with your game modes and robot types. I would rather have 5 interesting, solidly built robot types on 2 different maps than 10 trivially different robots on 20 trivially different maps.
• Consider progression / stat tracking: people will want an account that allows them to queue with friends, keep track of scores, earn a reputation (see: Elo), and chat on forums.
• If you want people to take it seriously and to have any significant player retention, there needs to be incentive to winning. Some examples, in particular order: Monetary; either real or in-game. Levels; you get access to new robots/loadouts/color schemes as you rank up. Ranking; Elo, MMR, division, etc. Cultural; make people want to win for the sake of winning and getting better (this one's hard).
• Community involvement is great. New robot / map contests, events, etc. keep people interested.
• Consider carefully the scope of your games, especially the pvp ones. What are the win conditions? How many players per team, and how many teams? Do games take 10 minutes, or an hour, or 24 hours? Are the player's social networks more like 'stacks' of 4-6 people, or clans of dozens? Do you expect players to play matches from start to finish, or will they be pickup style? These questions determine the "feel" of the game, and subsequently the behavior of your players. If you expect players to stay an entire game, and penalize them for leaving (CS:GO, MOBAs), the playerbase will take the game more seriously across the board and actually attempt to win. A pickup-style game will result in a TF2-esque situation where the vast majority of players are just messing around.
• I mentioned it earlier, but generating a deep enough game to have a competitive scene would be AWESOME. Imagine, teams of 10 or so, 3 in a command bot and the other 7 in various types of smaller robots. Strategy, tactics, surprises, twists! I would watch this so hard.
• You need to consider how you are going to deal with abuse. You will run into 2 types of abuse: reckless robot use and bad manners (often called BM). People WILL drive robots into walls, push arms on a weak axis, flip robots, etc. etc. They need to be very well built to not take damage despite 24:7 use. If a robot flips, will a person come right it? Does it get left there? Either way, the flow of the game gets interrupted. As for BM, what do you do if 3 people gang up on another and pin them in a corner? Will there be moderators, either staff or community? How do you prevent moderators abusing their power? What are the consequences for BM? (Examples: ban, low-priority queuing, time-out, mute, warning system)

Sorry if it is a little rambling. I'd be interested to hear your answers to any of these questions, and discuss them, but really I am suggesting these as things to consider long term as you build up the system of your game, as establishing yourself and keeping players onboard are something very few games succeed at.