I greatly prefer the Gen4 over the Gen3's and I have numerous Gen3's.  I have medium sized hands and I could not reach the mag release on the Gen3's without breaking my grip.  Not an issue on the Gen4's as I can reach the release but I do prefer an extended release.  I also prefer the texture of the Gen4 over the Gen3.  Hated the RTF versions.  I also like the dual recoil and prefer the impulse.  Many do not notice a difference, but I can easily distinguish the difference.  I really like it in the Gen4 G21.  I had one of the earliest or first 1000 run of the Gen4 G17 and it did develop a brass to face issue.  I ran over 25K rounds through the weapon before I changed out the RSA and ejector and that made a big difference.  Had video on it, but it is no longer. 

I like to swap sights, go with a minus or 3.5, standard spring and a polish job.  Yes the trigger will smooth out with time, but not as effectively as a polish job IMO.  I can definitely live with a standard 5.5 out of the box but I can do all the way up to changing trigger geometry and getting down to about a pound and a half if I chose, but that is not my preference.  3lbs minimum is about where I like to be.  Ironically several years ago during one of my Glock armorer recert courses, Dennis Tueller who was the instructor actually taught me the technique to accomplish the really light trigger.  I ran my Glocks for many years with non modified frames and did very very well with them.  Now I personally like to do a full custom hand fit where I remove finger grooves, slightly reduce the backstrap, undercut the trigger guard, radius the trigger guard, flare the magwell and texture the grip.  The beauty of the Glock is similar to the AR where you can easily and effectively (if you know what your doing) alter the weapon for a true hand fitted pistol.  Cost, easily customized to fit to the shooter, accuracy and reliability and it is hard to beat a Glock pistol.

Any suggestions on Glock armorer course? I was considering the Frontsight one. (Timing not good for me just yet so will skip the coming one).
And also books/DVDs that you feel give decent information?

Dang, dude you just gave me extra points on the PRO column to just get the Glock 21 Gen4 instead of a 1911... LOL

The Gen4 Glock 21 is an amazing pistol and I highly suggest it for a .45 pistol.  I own multiple Glocks and multiple 1911's and while I love both types, IMO comparing the two is not quite apples to apples.  They have very different personalities so to speak and I would select different ones for different applications.     

Any suggestions on Glock armorer course? I was considering the Frontsight one. (Timing not good for me just yet so will skip the coming one).
And also books/DVDs that you feel give decent information?

Most competent instructors who are highly knowledgeable on the Glock pistol platform and had formal training can more than likely give a good basic Glock armorer course due to the simplistic nature of the pistol.  An advanced armorer course or a doing custom smithing work may be another story.  Having said that I am not a fan of Frontsight, so I cannot not suggest them for anything firearms related.  The biggest draw for Frontsight is that they are near Vegas and legal brothels.  Guns, gambling and sex may sound like a great thing and I am not disagreeing if that is someones thing, but on that 3 item list, the firearms related training would have to be #10.  I would think that the Frontsight instructor has been through the Glock courses but this is not a guarantee, however being recognized by Glock as a certified Glock armorer is a good thing, especially when getting certain parts and factory support, so I might suggest taking a Glock course for the base foundation.  Also $500 for a one day Glock course is a bit steep. 

As for books or DVD's I have nothing to offer there.  There is a good deal of quality information via online content if you can filter out the large amounts of crap.  There are some online firearms forums where you can be assured of the quality of information that you are getting from certain forum members.  Unfortunately there is a steep learning curve for filtering crap via online content.

I am left handed so without a doubt i chose the gen 4. Iearned how to shoot with a gen 3 and never really liked the grip. But after holding then gen  4 in the gun  shop it felt like the grip was maybe a little bit skinnier  and felt better than the gen 3.   I bought the g22 gen4 and it was very reliable right outta the box.   I ended up polishing the trigger . Installing a lone wolf 3.5lb connector and a phanton adjustable trigger & bar. The trigger is smooth light and crisp. And 5000 rounds later still reliable.   The biggest problem i had with glock is the cheap plastic trigger. The safty sticks out and digs into your finger so with an aftermarket trigger the trigger safty will depress all the way and sit flush with the face of the trigger.

First experience ever with a glock was with a second generation.  It just felt terrible in my hands.  It wasn't anything close to the way a p220 or even a full sized xd felt.   However a year ago, I was at Young Guns, and asked to see a gen 4 g17.  That thing felt like it was made for my fat hands.  The grip texture was spot on, and it just felt like a "natural pointer" for me.  Glock had a lot of issues when the gen 4s came out, but they seemed to have fixed all of them.  I was a bit hesitant to buy one last year after reading a lot of the negative reviews on the gen 4s, but I found articles online that gave you the numbers for the correct recoil springs, and correct extractors.  So I popped off the slide, made sure everything was correct, and haven't had one problem to this day.  . Since then, I bought a g22, gen 3.  The gen 3 is ok, but it doesn't fit my hands as well.  With all that being said, my standard glock mods are....extended slide release,  extended mag release on gen 3s only, and a 3.5 lb ghost rocket kit, light weight striker, and after every cleaning, I give it the $0.25 trigger job.  I didn't mind the sights, however I did change them out, but only because at the time the tritium sights I wanted were on sale, so I picked up a few sets.