Well, I am an "old" player of DoTA, considering that the fact that I played dota since DoTA version 6.27 comes up, and ya, I played over 34 DoTA maps ermm... starting 5 years ago. However, I didn't take DoTA seriously until DoTA 6.40, when the existence of AI + arises. The AI are much tougher than human player and also the previous AI map, and thus because of that, I started to notice changelog and guides to think of a way to beat BMP 's DoTA AI...
And many scary changes occur since then...to the point I wanna scream at icefrog and say WTH is this! But well, I still play DoTA right now...ok, let the list begin...
Dagger (of escape?)
One of the biggest change in DoTA history, unarguably. This had caused so much stir probably in league game...Just to let you guys know, blink dagger used to be
KELEN DAGGER OF ESCAPE- blink to target location
-30 second cooldown
Now, it is
KELEN DAGGER (because it's hard to escape)
-blink to target location
-CANNOT BE USED if the user received damage in 3 second
-21 second cooldown.
Comment: In the long run, it's really a balanced change. In the old version, most hero are unkillable as long as they have a blink dagger, imagine you screaming when you are 1v1 with an enemy hero and when the hero almost dies he just blinked...And imagined a hero accidentally encountered 5 enemy heroes, and the when hero almost died from all the nuke, he just blink away with dagger escape. Imagine how mad they can be
Now, it is impossible. And maybe due to dagger nerf pub player started to favor lothar edge...
Bottle
(the old icon)
This change was a nightmare to ganker hero, but maybe it is a must ...
Old Bottle-700 Gold
-Heal 200 HP and 135 mana (when it first introduced) per usage
-after using rune in bottle, the amount of charge left in bottle is 2 instead of 3
current Bottle-600 gold
-Heal 135 HP and 70 mana
-after using rune in bottle, amount of charge in bottle = 3\
-autofill in fountain

Comment: Frankly, this change nerf bottle, imagine before this, 135 mana regen and 200 hp, in early game, a 135 mana heal means another nuke, and 200 hp is really nice. It's a dream item for spammer...But with the changes of bottle, nuker had to constantly rune whore to get a good supply of mana...I don't really like this change, but i continue buying bottle even now. The good thing is, now the bottle price is reduced, you can start the game by buying a bottle straight ( not recommended though)
Agnahim Scepter
This blue color dagon really changed a lot. If you are playing dota one year ago, people will laugh at you when you buy this blue color dagon to Jugg, but now, they won't
Old scepter-requires soul booster and mystic staff
-gives 500HP, 400Mana and some intelligence point and regen
-does not improve ulti of STR heroes and MOST agi heroes (except luna and venomancer)
Aghanim's Scepter-requires blade of alarcity/staff of wizardy/ogre axe + point booster + recipe
- add 10 to all stat, also provide 200 HP and 150Mana
-improve a lot of hero's ulti (sandking, butcher, and even earthshaker
Comment: A really nice change, and the change of recipe makes it viable to most heroes, it promotes better gameplay. An overall nice buff, the only minor bad thing is, it doesn't provide more stat compared to the old scepter. But well, you pay less for it now, so no complaints
Sentry ward
I know you guys might not notice, but this item change cause some stir in high level tournament, when warding is everywhere. The change of sentry ward, at one point, makes my friend say " Invi hero now rules the world"
Old sentry-last 6 minutes
-has a bigger true sight range
New sentry- last 3 minutes
-lower true sight range
Comment: With these change, heroes like rikimaru and broodmother will be

, with the decrease of duration, invisible heroes can farm longer in a lane, as opponent need to buy more wards to counter those invi bastards and lothar edge uses...>.< . But maybe icefrog has heard enough complaints of ward-nerf, so this item is introduced to shut those people up.

" I wish icefrog change his mind someday T.T . Gimme back the old sentry ward. "
Black King Bar
This item is the only hope for dps hero to prevent those nasty nukes and stuns, and this is the item that made most intel hero shrieks in horror. In a decent level dota game, you will always see black king bar, and a hero with bigger look, shouting " FOR KHAZ MO DAN!"
Old Black King Bar
-(the recipes change few times for this recipe, so i don't remember)
-a constant 10 sec magical immunity
-cooldown 90 second for constant
-change some hero into some funky look
-activation grant 10 dmg

- Tinker with BKB @.@

- Obsidian destroyer with BKB
New black king bar
-magical immunity reduced from 10/9/8/7/6/5
-cooldown from 80/75/70/65/60/55
-after 5 uses it became 5 second magical immunity and 55 second cooldown
-no more funky hero look T.T
Comment: This item no longer makes dps a scary unkillable god. The fact that BKB reduces it's effect after each use suggest that you cannot activate BKB just for fun. And to be true, I hate this change...it simply makes troll more susceptible to nuke if you fail to benefit in 5 second. But well, same goes to enemy too...
Part 2 - hero change come soon