Ok, so I have a friends who's a huge fan of 3.5 and he's now playing Pathfinder. I've never played 3.5 neither Pathfinder, I've only played 4e and 2nd edition, but now I would like to switch to 5e because I'm really enjoying the basic rules. I wanted to invite the friend I was talking about to the table, but he insists that now that he has been reading the Basic Rules it' clear that 5e is just 3.5 with insignificant changes. so I would like to know if this is true since I don't know about 3.5 rules.
What do you think so?
I think that your friend is correct.
Having read through the 5E Basic rules, they strike me as being very close to 3.5E in most ways. The largest "changes" aren't really what I'd call changes at all - they're restrictions on various options; things you can't do in 5E Basic that you could in 3.5. These largely seem to revolve around proficiency bonuses taking the place of various BAB, save, and skill point progressions. Throw in a few things like no feats in Basic, and that's the majority of what's different.
Some things are imported from other sources; sub-classes are the natural extension of alternate class abilities from the later 3.5 supplements (and pretty much whole-cloth use of the class archetypes from Pathfinder).
The changes that seem like actual changes are the advantage/disadvantage mechanic, doubling the number of saving throws a character has (adding in Strength, Intelligence, and Charisma-based saves alongside the existing Dexterity (Reflex), Constitution (Fortitude), and Wisdom (Willpower) saves), and the slightly-altered manner of preparatory spellcasting (and ritual spellcasting, which is a 4E-ism).
There are some other differences, such as elves having full-on darkvision, and the ability score caps (and ability score requirements for multiclassing, which we won't see until the PHB comes out - which is a 1E/2E-ism), but for the most part these are details.
Save for the aforementioned "actual changes" I mentioned above, 5E Basic really seems like a 3.5 rules set where most of the bonus progressions were restricted to the level of an E6 game.