So it may be just me but my players seem to be enjoying these homebrew not 20 rules. Want to see what the other DM think. 

initiative: a nat 20 will give you a bonus surprise round where as a nat 1 will loose you the 1st round 

Spells: on spells that require a save or take half a nat 20 no damage is taken and a nat 1 double damage 

 I do like the nat 20 and 1 in fighting but feel like it's only usefull on skill checks and attacking and wanted to be able to use them in other aspects that roll a d20

Tell me what you guys think 

I've used those rules in many different games in various combinations, and they work just fine as long as everyone is on board with it.

The initiative rule, I ended up dropping after a conversation with a fellow DM. A nat 20/1 already puts the player/monster in a very good position so in most cases the added benefit/detriment is lost. For the sake of certain class features, like assassin rogues, having that super fast reaction time to hit the top of the initiative is paramount to their strategy. To be beat out by a mere goblin might feel cheap. That is not to say that it doesn't make sense in the narrative, or in practice; I've managed to surprise my martial arts instructor a few times by reacting faster, and in a different way than he anticipated.

I've never found a good way to use 20/1 rolls on a save spell, either I felt like I was encroaching on the abilities of a class (evasion, dragon's resilience, etc.) or it didn't make sense. How do you use a nat 20 on a save/suck spell. If a creature rolls a nat 20 on a spell that causes fear, do they become immune to that fear longer? If you roll a nat 1 for the dex save on earthquake, are you more prone? Thunderwave, for example, you have increased/decreased damage and distance pushed, so in some cases it's easier to figure out the answers to non-damage effects.  Now this is simply trying to make it so the nat 20/1 rules affect everything, and not simply damage rolls, so those questions are made with some sarcasm. I'm probably overthinking it in the long run, I usually do.

In the end though, have fun with those rules, it does add some spice to a rather bland dish.

thanx man I do enjoy all feedback 

I hadn't thought of expanding the - non-official - critical success/failure rules to saving throws and initiatives - although we do the "double damage dice" on Nat20 attack rolls and "lose your weapon / break a bowstring " ( or other bad thing ) on Nat01 attack rolls.

I kind of like the idea - although I will have to consider DMThac0's counterpoints. I think with saving throws, I'm content with the idea that sometimes there just isn't a benefit or penalty for those natural extreme rolls ( you can't fall off the swaying bridge, or stay on it more ). That might not prevent me from applying those when it makes sense logically.

it may not work mechanically but it great for the rp. but will post when i come into issues 

Initiative: Whoever rolls a 20 is already in a good place and generally, there is no surprise in most encounters. 

Spells: If a 20 gives no damage, then a 1 should yield maximum damage, not double damage.

The version we do for initiative is that natural 20 gives you advantage on your first attack roll and natural 1 gives you disadvantage on it.

Ok so with saves and stuff like that it is either a success or a fail there isn’t really anything else

Quote from TexasDevin >>

The version we do for initiative is that natural 20 gives you advantage on your first attack roll and natural 1 gives you disadvantage on it.

 I like this idea

Okay, so when it comes to saves and such, there really is not much more that can be said; it is either a success or a failure.

My house rules are:

Battle Impulse/Battle Hesitation: A Nat 20 on initiative grants you advantage on your first attack and automatically makes you first in the round. A Nat 1 gives disadvantange on the first attack and automatically makes you last. 

Critical Saves: A Nat 20 on a save spell grants 1/4 damage as opposed to half. A Nat 1 doubles the damage. 

Critical Effects: A Nat 20 on an attack grants an additional effect - i.e. a Nat 20 guiding bolt also blinds the creature until the end of their next turn (radiant), firebolt burns the target for one additional damage dice at the start of their next turn (fire), chilling touch gives the caster temporary hit points equal to one damage die (necrotic), etc. These can apply to save spells too but perhaps not all. 

Honestly it depends on your group entirely.

I have one group for example who are so extreme into the roleplay that they push, bend and break the 'rules' as often as possible. Trying to present the challenges that they ask for makes my job so much more difficult, but it all still works. Your system would work amazingly for that group.

I have another group who actively need the rules as a guiderail to help them be less chaotic. Without the rules as a guiderail they simply would never have the motivation or need for their characters to actually do anything during a session. For that group, too much homebrew basically means that they get decision paralysis.

My other two groups are pretty much middle of the road on this. They are a elements of both of the previous two groups. Yet, your houserule wouldn't work for them either I don't think. 

That's ultimately the rub, is that it will entirely depend on the group you're looking at. The way you handle them seems pretty fun though.

Quote from Zyrrel >>

My house rules are:

Battle Impulse/Battle Hesitation: A Nat 20 on initiative grants you advantage on your first attack and automatically makes you first in the round. A Nat 1 gives disadvantange on the first attack and automatically makes you last. 

Critical Saves: A Nat 20 on a save spell grants 1/4 damage as opposed to half. A Nat 1 doubles the damage. 

Critical Effects: A Nat 20 on an attack grants an additional effect - i.e. a Nat 20 guiding bolt also blinds the creature until the end of their next turn (radiant), firebolt burns the target for one additional damage dice at the start of their next turn (fire), chilling touch gives the caster temporary hit points equal to one damage die (necrotic), etc. These can apply to save spells too but perhaps not all. 

As long as your players know these rules during character creation then it is possibly fair.

Do the monsters abide by these rules as well?

Yes, all players know all the rules going in. And, as a matter of practice, all rules equally apply to monsters as well. 

Quote from Ultimer >>

Ok so with saves and stuff like that it is either a success or a fail there isn’t really anything else

 once I created an NPC called The Wise Man. he had a bunch of stuff going on, but his main thing was he had 838237948174384719847 wisdom and 10 everything else. he used to ba an adventurer and he rolled SO high on a wisdom save against true polymorph that the spells reflected and hit the evil wizard who cast it. you could do something like that