I watched chunks of the first video. It's kinda funny watching games from the older metas, seeing as how drafting is completely different now. Some notes/comments:
- Draft analysis isn't too bad, but needs some work. For example, you should always strive to explain what the lineups are capable of, both in terms of what they're gonna look to do (gank, push, 4-protect-1, etc.) and how the teamfights will shape up (i.e. "They have great initiation with Clockwerk's Hook, after which the enemy team will be forced to gather or sacrifice their teammate").
- You sounded unsure of yourself when predicting the lane configurations during the draft. Whenever you're not sure how they're going to lane it, just list the different possibilities while explaining the strengths/goals of each.
- Radiant ended up aggro trilaning; make sure to elaborate on why they would make that decision, and what can be gained out of it (usually either killing or disrupting the enemy carry's farm)
- You criticized the Alch for his skill build several times. It's ok to voice your opinion or to question something, but there was a point when you were basically berating him. Try to keep negativity in casts to a minimum, cause it only invites people to question your own ability.
- Part-way through the cast, you were kinda jumping around the map saying "boring, boring, boring". Even if you're not aspiring to be a play-by-play caster, you should at least try to liven up the game, or to sound genuinely excited about plays (when first blood came out, you sounded nonplussed. You could always spruce stuff like that up with something like "And ______ gives up the First Blood, going the way of _______. Mythical Penguins are off to a great start in game 1 of the series.")
- In the same vein as that first blood example above, try to mention team/player names whenever you can. It helps keep the viewer involved in the game and encourages narrative ("Loda dies again! Pieliedie's mission in this game is to keep Loda down, and boy, is it working!").
- Any time there's a lull in the game, make sure to bring up the different graphs (Last Hits, Net Worth, team XP, team Gold) to help portray the state of the game. Again, try to explain what each team wants to accomplish with their lineups.
- Some of your commentary was a little inaccurate, but that's not too bad since it'll only get better with time and familiarity.
- If you're looking to be more on the play-by-play side of the fence, make sure to describe the action, step by step. ("Morphling dives in with a Waveform! He's looking for Clock! Clock is juking through the trees! Morph is microing his Replicate to cut off both exits!", etc.) Watch some Tobi/LD replays for examples of teamfight casting. If you're more interested in being a color commentator, try to find a casting partner who can take on that main caster role while you explain strats during lulls. Also, keep studying pro games to broaden your game/meta knowledge.
I didn't watch all of it (watched ~30 min), but you have potential. I'd say the biggest thing you have to work on is learning how to make things sound exciting (again, watch VODs of the top casters). Hope that helped a little?