First off: I'm aware, this may sound more critical than is warranted, especially since it's your game, and many of your changes are more a matter of taste than 'balance'.
Still, while you're saying you're rather familiar with 4e and already tested some of these rules, I'm wondering if you first tried playing 4e as is, i.e. without any houserules first?
With that in mind, here's my comments:
Achievements: I don't really care for these; they feel too video-gamey for my taste, but I can see how some players may enjoy that kind of thing, so that's fine, I guess.
Critical Successes and Failures: I'm a big opponent of having a flat 5% chance for critical failures. It's way too high. Have you considered that Controllers and characters with AE powers will be suffering from critical failures a lot more often than other classes? Having said that, I like your approach better than most.
Saving Throws: Are you sure you want to play 4e? (Just kidding! [mostly]) Turning saving throws into a defence was a change I welcomed very much. When we started playing Pathfinder last weekend, I was painfully reminded how much I dislike doing them the old way. But that's just a personal preference, I guess.
However, I'm going to predict something: It won't take long until you drop the rule about all those additional saving throws. You're turning D&D into Yahtzee!
Have you already played 4e? There's already plenty of dice-rolling as it is. In Paragon Tier, it isn't unusual to roll four or five saving throws every single turn!
Technology: *yuck!* Entirely a question of preferences, though.
Power Swap Feats: Bad idea, as others have already pointed out.
Leveling: Well, in my 4e campaign, I got rid of XP, entirely - at least from the players' viewpoint: I still use them to calculate encounter difficulty, but the PCs level up when they reach a story milestone. It doesn't matter how many xp they'd have gained using the official system. The obvious advantage is that they're totally free in deciding how to approach problems: If they manage to reach their goals without engaging in a single fight: more power to them.
Personally, I enjoy leveling up often, but I think leveling up once per 1-2 sessions is too fast: It takes some time to test your new powers, figure out if they work for you and get used to them. You simply cannot do this in as little as one session. You'll end up with players that don't know how to play their characters effectively, because the characters are continously changing and evolving. They'll spend more time reading their powers than playing.
Class Alterations: I don't see any problems here.
Injury Rules: Again you seem to dislike a concept that is central to 4e. Having said that, in our group we've experimented with this, as well, e.g.: We enjoy overland travel/exploration themes, so we ruled that while on the road, character do not recover the full amount of healing surges. So, 'random encounters' are a thing to be feared again. We've also used the concept of 'waves' of encounters at some points: Basically, it's an extended combat encounter without any opportunity for a short rest in-between. All the characters get to recover between the 'wave' encounters is a single encounter power.
Anyway, back to your idea about injuries: I'm not sure if I understood your idea correctly: So, anytime a character takes damage larger than their bloodied value, they'll have to make a death saving throw, and if they fail, it reduced the number of death saving throws they may fail before dying? Is that it?
First, I'd like to note that this is only ever going to happen when you use 'Lurker' monsters. No other monster role could potentially deal sufficient damage. Second, you should be aware of the effect it will have on your players: I'm almost sure they'll do whatever they can to avoid having to continue adventuring if they have any kind of injuries. If this is exactly what you have in mind, then go for it.
It does seem to be a bit at odds with your desired leveling speed, though, unless in actuality, it's going to be handwaved: "Three days pass, you're all fine again." Otherwise, it may result in sessions with little progress being made.
To reiterate: It's your game, of course. I'm just trying to put myself in the shoes of one of your players, and how I'd react to these house-rules.
