So, I had this in the homebrew section but thought I'd get some fellow DM opinions.

I am thinking of bringing this homebrew house rule for counterspell to my game (I got the idea from Davvy Chappy). The reason for doing this is that I found myself creating encounters based around that spell. It burns through reactions and it just turns into a game of who can cancel out the spell the most (enemy casts fireball, counterspell, well he also casts counterspell, well now the warlock is counterspelling his counterspell, etc).

Here is the idea:

When counterspell is cast each character rolls a d20 and add their spell casting modifier plus a modifier equal to the difference in spell level (ex. if the counterspell is lv 3 and the spell is lv 1 the caster gets a +2 on the account that the counterspell is a stronger spell. But if the counterspell is lv 3 and the spell is lv 5 you get a -2 because you're trying to beat a stronger spell). If the caster of counterspell wins, their spell goes off and the opposing mage's spell fails. If the target wins they manage to harness their focus and push the offending mage's magic (counterspell) away from their spell. 

I was also thinking that this could add some interesting flavor to combat when it comes to spellcasters. When I showed this to my group the Wizard, of course, had a problem with this because he felt that I was taking something away from his character. His argument was that he doesn't get any other reaction and that counterspell is one of his only defenses. He also made the argument that people build their characters a certain way and taking something that is an instant success, like counterspell, and making it more a chance of the rolls, takes away something the character worked hard for. I tried to explain that the higher level you are or cast the spell the more modifiers you get, therefore allowing more of a chance for success-but he was like there's still a chance of a 3rd level wizard defeating an 8th level wizard and that it wasn't fair. 

What are your thoughts?

Update: I'm considering keeping the auto fail for 3rd level and lower but keeping the contested roll for higher level spells. 

I think this is not needed.  Most importantly it ignores the many many ways to deal with counterspell.

Ways to stop me counter-spelling that my DM has used against me:

1. Counterspell the counterspell as stated by you.
2. Invisibility ("1 reaction, which you take when you see a creature within 60 feet of you casting a spell)
3. Subtle spell by a sorcerer - again see them casting
4. Globe of Invunerability
5. Be 61 ft away.
6. Firebolt cantrip cast and counter-spelled, followed by a QUICKENED Hypnotic Pattern.
7. Attacking me with more mages - i.e. big bad villain has 4  apprentice mages.   Everyone is dressed exactly the same, no 'kill me first' decoration on the master mage.

If you do not allow them to omnisciently know the identity and level of the spell being cast, Counterspell is much less effective. For instance: 

"enemy casts fireball, counterspell..."

How did the person countering know it was fireball? RAW there does not appear to be any way. XGE has the only rule I know of about identifying enemy spells, and this ID requires an arcana check made as a reaction. You only get 1 reaction, so if you burn your reaction IDing, you can't use counterspell. This means, at least in terms of RAW, counterspell would have to be done "blind" -- you see a mage about to cast, and you cast counter-spell because you think it will be bad. It may turn out to have been fireball... or mage hand.

I actually allow a variant someone on this forum suggested, which is to let the person doing the reaction, if they succeed, use counterspell as part of the reaction. But that's a house rule -- you don't have to allow it, and if CS is mucking up your game and unbalancing things, I wouldn't allow the house rule.

Also... if the monsters are intelligent, do what the PCs would do. The second you see someone on the field cast counterspell, that person becomes target #1, and the monsters go after the counterspeller until he or she is down for the count. They bad guys will know this person could hamstring their casters, and would stop it.

IMO, counterspell should paint a huge target on your back for any intelligent enemies.

Quote from BioWizard >>

If you do not allow them to omnisciently know the identity and level of the spell being cast, Counterspell is much less effective. For instance: 

"enemy casts fireball, counterspell..."

How did the person countering know it was fireball? RAW there does not appear to be any way. XGE has the only rule I know of about identifying enemy spells, and this ID requires an arcana check made as a reaction. You only get 1 reaction, so if you burn your reaction IDing, you can't use counterspell. This means, at least in terms of RAW, counterspell would have to be done "blind" -- you see a mage about to cast, and you cast counter-spell because you think it will be bad. It may turn out to have been fireball... or mage hand.

I actually allow a variant someone on this forum suggested, which is to let the person doing the reaction, if they succeed, use counterspell as part of the reaction. But that's a house rule -- you don't have to allow it, and if CS is mucking up your game and unbalancing things, I wouldn't allow the house rule.

Also... if the monsters are intelligent, do what the PCs would do. The second you see someone on the field cast counterspell, that person becomes target #1, and the monsters go after the counterspeller until he or she is down for the count. They bad guys will know this person could hamstring their casters, and would stop it.

IMO, counterspell should paint a huge target on your back for any intelligent enemies.

 I like your points here and may drop the homebrew. So, lets say the warlock uses his reaction to identify the spell. Can he than tell the wizard so he can use his reaction to counterspell? How would you handle that situation?

 I like your points here and may drop the homebrew. So, lets say the warlock uses his reaction to identify the spell. Can he than tell the wizard so he can use his reaction to counterspell? How would you handle that situation?

I would allow it, yes. You're burning 2 reactions to do one counterspell... that will leave both of them with no additional reactions to take later in the round. 

Again it is an example of how an intelligent enemy could decoy the 2 of them into burning reactions and then having none left when the REAL bomb is thrown.