i remember in 2e there being amounts of time (I want to say counts on initiative) to cast so you start on a 7 but end on a 4 and in-between it can be stopped... am I remembering that right...maybe it was even a house rule.I don't mind Counterspell as a near-zero-cast-time spell in itself, but with that said:
--- all spells should have casting times a la 1e-2e, even if that time is near zero in a few cases, and be interruptable during that time
--- Counterspell should never be able to counter another Counterspell*. This isn't M:tG with its silly last-in first-out stack, it's D&D where things (should!) progress in linear time, meaning that by the time you finish casting your Counterspell mine has already gone off. Intended end result: no counter-counter wars like you see in M:tG.
--- casting Counterspell uses a spell slot (2nd level in my game) just like any other spell, meaning you only get so many in a day; but if your timing is right it's guaranteed to work. Note that in my game you can only cast spells of a level by using a slot of that level, meaning if you're out of 2nd level slots you can't cast any more 2nd level spells for the day, period.
* - or any other zero-cast-time spell, of which Featherfall, Command, and a few Power-Word spells are the only ones I can think of quickly.
(we actually house ruled initiative to be d20 highest go first in like '96 we just switch dex mod from a negative to a positive)