I started playing in 2011. This was just after the New Phyrexia prerelease. The 2011 Commander deck precons were still a month away. The format had just recently been renamed as Commander; formerly being EDH. The Command Zone had just become a thing within the official MTG rules. And Commanders had just been given that moniker having previously been referred to as your "general".
I don't
recall a lot of specific cards that were played at the time (aside from those that would go on to become format staples). Although I do
recall all of the [Color] Sun's Zenith cards getting a lot of play. They are from
Mirrodin Besieged, which was the previous set.
Red was considered the worst single color, not white. Blue was considered the best.
There was no
Arcane Signet. Talismen had not been reprinted. Neither had the Medallions. Ramp consisted of Guild Signets,
Rampant Growth if in green, and then a lot of 3-mana ramp. I do
recall Darksteel Ingot being very popular.
Gilded Lotus was a good card back then.
Also of note:
Command Tower didn't exist yet. Not until the 2011 Commander decks hit. And even then, if you didn't buy one of those precons, then you still didn't have one. It followed much the same pattern as
Arcane Signet. All the Commander players wanted one for every deck. But few available to purchase as singles.
The rules were a bit different back then. The Legendary rule affected all permanents on the battlefield. And if more than one player had one, then all were put into the graveyard. So if you have a
Mayael the Anima in play; and then I play one, both are sent to the graveyard. Same with Legendary lands like
Gaea's Cradle. For this reason, legendary cards in the 99 were something to use sparingly. Because they wouldn't stick around for long. A legendary in your deck was often there as spot removal against that same commander.
Phantasmal Image was a very popular (and powerful) card. Under the old legend rule, it basically says "a commander of your choice gets sacrificed".
The tuck rule still existed.
Terminus was great removal for troublesome commanders. As was
Chaos Warp when it debuted in the 2011 Commander decks.
Board wipes were the preferred mode of removal. Spot removal was used, but in much less quantities. It was not uncommon to see a board wipe in each turn cycle. As one player recovered quickly, another would wipe again.
There were a few other rules difference. Obviously, there were no commander death triggers. Given that rule just changed recently.
Your deck also couldn't make colors outside of your Commander's own color identity. This doesn't come up often currently. But if it still existed, a Commander like
Ragavan, Nimble Pilferer wouldn't be very good at all.
There have probably been some other changes. But the biggest change I think from 2011 to now is PRICE. The Modern format had not been introduced yet. There were no made-for-commander cards yet. Everything still filtered through Standard. If you waited until cards rotated out of standard, most cards were cheap (aside from the OG duals). Quite often good commander cards were cheap even before rotation. As a general rule, good Commander cards were not good Standard cards.