Quick rundown of DVD flashing and related concepts. I will be ignoring the king kong hack.
First there was DVD flashing, it was a dark time and over quickly enough which went into the (i)xtreme era.
The early ixtreme era was simple enough with most of the trouble coming with new DVD revisions and methods to dump keys (give or take some hardware efforts earlier on in some revisions this was trivial right up until the liteon 7 series).
Versions ticked along with bugs being fixed, new drives being released and yeah.
Somewhere along the line people decided, in deference to tradition, that they should be able to play their copied games/hacked console on the online services for them and thus the "livesafe" mindset was born. At first this manifested as the low speed firmwares being removed (the 360 DVD drive runs at 12X but on some models that sounds like an engine just started up in your room). You might have been ejected at this point.
Part of this livesafe stuff was checking the games in the drive to make sure they complied with what was known. For better or worse this meant that when new games came out with new waves (waves happened in response to the update bundled with the game) they might be flagged as bad burns and would not play. Most people just updated when this came along but this also led to wave patching which made newer games use older waves and thus be able to be used in the relevant firmwares.
Later firmwares also had a so called activate.iso which made the DVD drive ignore its checks for that boot. Nicely enough we also got a hacked version of the firmware known as 1.6NS which always ignored the checks and worked with everything until things got really odd.
There was also ixtreme LT which hit shortly after 1.6NS and solved this problem for good by also disabling checks. The problem with LT though was it required splitvid which was largely absent from early games (and early burns) and a handful of later ones as well so not everybody jumped to it. LT also meant extracting serials if you did not have them was not really doable with a further hack (like JTAG).
The rise of AP2.5, AP2.6 and such like. Originally just 6 games (give or take a few quirks here and there) but that did include a COD, a halo and other games fans of multiplayer go in for. There were some quirks with beta dashboards and such that allowed you to still run a handful but eventually if you wanted this you would have to upgrade to LT and reburn. As newer games were coming out that required later dashboards (but not necessarily a DVD update) you faced not being able to play those games, seen as the original AP2.5 titles were largely online things this was not so troubling.
MS played hack, counter hack for a while here and they finally lost that battle with an update to LT and a final reburn.
The rise of XGD3. Technically all XGD3 games sport some variation of AP2.5 but that was kicked in the head as part of getting it to work. For various reasons MS introduced a new version of their disc format which meant most drives had to be reflashed with a new firmware by MS to work with it. It took a long time between the beta and the first games to use it though so it was sorted quickly enough. More troubling is it can not be burned by normal drives so you will need a special drive to burn it (consider the odd cuttoff/overburn stuff a nonworking method of the past), originally this was a short list of drives and predictably they got quite expensive. Nowadays there is a more annoying softmod method (you have to run a program when you want to burn it) but they are slightly easier to get your hands on.
Not every new game uses XGD3 but if it is a notable one you can be reasonably certain it will.
On Deus ex. lisreal2401 is half accurate here -- the scene release of Deus ex and many releases around the world legitimately did not feature the update that reflashed DVD drives. However there were other releases in various places that did feature the update. Basically every game since will do the update and you will not be able to get around it with your current setup. RDR GOTY is definitely in this category, original RDR less so.
Along the line the xbox slim got introduced and with it a whole new load of drive models, now we get things like the kamikaze mod, replacement boards and more but in terms of MS moves beyond that there was nothing really.
Also along with all this there came ODDEs which act like a DVD drive but instead direct reads to a USB drive, they are good but quite expensive.
It was killed in the August 11th 2009 update but there also came to pass the so called JTAG hack. Assuming you have a parallel port and a tiny bit of soldering skill you can do this with about £10 and a trip to maplins (a few diodes, some wires, maybe some resistors and you are golden). I know it is a RROD recovered 360 and so quite likely to die but a JTAG machine is a very nice thing to have.
Somewhat later an equivalently powerful hack known as RGH appeared though it requires actual chips and proper soldering, what dashboard you are on troubles.
Links as just to make this a tiny bit more complete
http://abgx360.net/verified.php -- nice listing of what wave goes with what. Anything above 11 reflashes it.
http://www.abgx.net/filename/?ch=6 will tell you when something was released and if it is XGD3 or not.
Finally I am not sure what goes as far as blocking JTAG goes (technically it is not the dashboard update but a related update) but you should be able to refuse updates as far as DVD stuff is concerned.
Assuming you do not want to play the AP2.5 games (Halo: Reach, Call of Duty: Black Ops, Call of Duty: Modern Warfare 2, Fable III, Need for Speed: Hot Pursuit and Assassin's Creed: Brotherhood) and are quite happy to stop at Deus Ex you could probably just about get sorted with what you have now if you are willing to fiddle with lots of isos. Personally I would consider it a waste of discs but to each their own.
On the other hand if you have your serial or just dump it as and when, do not care about JTAG or RGH (they really are quite nice but again if you have an RROD fixed board its lifetime is typically measured in weeks) and a compatible chipset (you can still just about buy a PCI card to do it with for about £5 on amazon -- via 6421) most of what I just said was a quick history. You will need to find something to burn the new games too. There is a good chance you will have to scrap your existing games (you can fix them with ABGX360 and reburn) if you do this though.
