Core Set 2021
Core Set 2021 is a fairly aggressive, straightforward 2-color format. Generally, decks contain 17 lands and are defined by synergistic commons and uncommons, as there are not too many bomb rares.
How quickly most games are decided.
Power difference between rares and commons.
M21 games are mostly driven by strong color pair synergies at common and uncommon.
Importance of cards working together.
M21 is not a complex set, but deck synergy is of above average importance to get the most use out of your cards and ensure wins.
As a core set, M21 is light on complexity and does not have any new or unique mechanics. But M21 still has strong synergy among cards with evergreen abilities.
Effectiveness of the available removal.
Most colors have access to at least one decent to good removal spell at common. There are also very efficient uncommon removal spells available.
White has Swift Response, which is at odds with the aggressiveness of the color. Secure the Scene is a very bad removal spell which makes White's removal much worse than the other colors.
Power balance between colors and decks.
M21 is fairly balanced between all of the color pairs, but being an aggressive format, Blue-Black control - and control in general - is somewhat underpowered.
How many lands and colors generally see play.
M21 is a fairly aggressive core set and abides by general aggressive curve rules.
Some hyper aggressive decks may want 16 lands, but you very rarely want 18 lands.
Ability to fix for more than two colors.
Possible but difficult
All ten gainlands are at common, so a single splash is possible but generally avoided, given the aggro nature of the format. There are also few cards that are worth the splash.
However, mana fixing is terrible in limited by default - so try to pick up an on color dual if you can!