Pass through capability, (like others disappointed with the thickness limitation, would really have expected 3/4") but, there are work arounds.
Cooling, as my place can get pretty hot during summer months.
Improved optics and power supply.
I ordered mine without the filter as I will vent outdoors, no near neighbors & no worries about smell with dairy farms nearby. 
I would have ordered pro for pass through first then better duty cycle. Not knowing what I was getting into, I figured the basic would keep me occupied for a while without pining for moar powah. I usually buy the high end in my tech purchases maxing out the add on but the basic would meet my initial and long term plans.
Pass-through was top of the list…the actual z restriction is…less than good but, we’ll see there. Extra power was just 2nd to this.
Not quite the same as most. The pass through slot was the thing that had me looking at the pro but it didn’t make me upgrade. I originally ordered the basic without air filter. But two things made me change. Firstly, and it’s been so long now my memory might be wrong, the pro came with the filter so it meant the pro was less to upgrade. The second was a conversation with a friend where he said, “If you’re spending all that money, why not spend the extra to get the better model”. As I’m in the UK, and shipping is a real issue, it made sense to go big from the start.
I don’t think I’d heard about limited height on the pass through. I doubt it will make a difference for me as I was thinking of using it to make leather playmats for TCGs however could someone link to that announcement or let me know what the height has been limited to? I imagine I am not the only person that missed it.
I’ve ordered the basic model, but there is a single reason I’ve considered the pro, and that’s the passthrough.
And the only reason I’m still going with the basic is the price.
The 1/4" limitation is now listed in the specs:
It’s also mentioned in many posts including this one:
For me it was the pass through slot and the fact that it is bundled with the air filter. I want to do lots of odd shaped stuff so it will really help!
Edit after seeing some of the other posts:
The cooling is also on my list for sure
I bought the pro model because I wanted the fastest and most reliable unit.
Here are the main reasons why in order of importance(most important first)
1.) Better Cooling (I really don’t want to have cooling problems)
2.) Better Optics (I figured this was important for better accuracy in the trace feature)
3.) Better Tube (Faster you say? Heck yes! I’m also sure I will find a need for those extra 5W)
4.) Pass Through ( being able to cut/engrave longer material 10" at a time is nice and I’m sure I will use this feature but honestly if the pro didn’t have the capability of a pass through I would have still purchased it. Perhaps if the pass through was a lot taller I would go nuts over this but not for 1/4" material.)
The better cooling and passthrough were the main selling points for me. Like many others, it gets warm here in the summer and the idea of having to stop prints less frequently is a big deal. Overall, I decided to upgrade a couple of months ago because I didn’t want to see all of the things people were doing with the passthrough and not be able to do it myself. If I’m spending so much, I want to be able to do everything the machine can possibly offer.
Originally:
1)pass-through slot
2)larger cutting area
3)Longer working time due to better cooling
Currently:
1)Better Cooling
2)Larger cutting area
3)Higher Power
4)Pass-through Slot
I’m still excited about the pass-through even though I was disappointed about the height restrictions. I’ve learned a lot while I’ve been here, and I think I’ll be able to cope accordingly
I got the Basic, strictly due to the price difference. The increased power and cooling are not really all that important to me, but that’s only because I will be using it 99% just for fun / gifts / etc, rather than as a business machine, and so I will not be running it all that much, nor will I need speed.
However, I would SO LOVE to have a pass through slot! The lack of that is a HUGE bummer for me with the basic model.
@dan: How about this idea for the hopper: Why not offer an Intermediate Model, which would have all of the internal components of the Basic, but with a pass through slot as well?! I - and I bet many others - would gladly pay a fair premium for that feature.
Edit: Omg, or even better: Offer the ability to custom order a la cart with different options, like when you buy a new car.
Upgrade to 45W for $XX
Upgrade to Pass Through Slot for $XX
Upgrade Cooling for $XX
Oh yeah; now we talking…
Of course, there would then probably have to be a re-stocking fee for cancellations…
Pass-through was biggest factor. I was only minimally disappointed by the 1/4" restriction.
Better optics and power was a lesser factor. The initial marketing, as I recall, was essentially up to 1/4" materials, which I took as not all 1/4" materials. As I want to use 1/4" boards from a wide variety of hardwood species, I figured maybe that up to will mean all the ones I want to use. Also, maybe it would help with cleaner cuts on leathers with various treatments.
The upgraded cooling is nice, but it didn’t play a huge role in my decision making. I guess I won’t know how nice it is until I see how much I use my glowforge.
I join the majority. Same as Takitus.
Always been for me:
I ordered the Basic. The biggest driver for me was the cost.
The features in the Pro that I’m most excited about, in order:
I always thought the Pass-through was cool, but I never saw a use for it personally. I was always planning on doing small projects. Once I found out the regulations on Class 4 lasers, I was glad I made that decision.
I do agree with @nunzioc though, it would be nice to have an a la cart option where you can pick and choose features. I would have jumped at the change to upgrade the cooling!
a la card would be great
but solid metrics to what each of these up sells actually gets us would be greater. then we can gauge for our selves and our needs what is of value and what we are willing to pay for that uptick
I got a Pro because in the description of the different models somewhere (I think it was labeled something like “Should I order a Pro?”) it said that it was going to be made for more continuous use, like in a makerspace or other shared use situation. I’m happy to have the pass through and plan to use it, but the heavier dutyness of the Pro is my main reason.
Take what Takitus said and apply it to me as well. He put it almost word for word the way I feel/felt.
I have grand leather working plans for the Glowforge, my Fiancé knows tailoring and I’m okay at leatherworking so I’d really like to try my hand at corsets and leather jackets and the pass through seems important for that, i’m also curious to try to build some modular furniture pieces out of MDF or HDF and Delrin. …and the longer warrantee 
Filter, stronger beam and cooling!