How worth is it to start this game now given how long it's been out?

The best time to plant a tree was twenty years ago. The second best time is now.

Catching up
In-game facility called Forward Basecamp that gives a bevy of items for raising Tactical Dolls (your main fighting force). Unlocks at Commander Lv.20.
Protocol Assimilation for steamrolling early to mid-game content. Unlocks upon clearing Chapter 7, Stage 5.
Newbie Career Quests that gives free preleveled units where some of them, namely AR Team, are meta viable.
Contents
The only permanently missable ones are mainly minigame cosmetics.
Major events? Campaign Missions. Banner units? None here. Collabs? Reruns are possible (Note: they're not gamebreaking).
Stamina
There is no stamina. But it has a rough equivalent in Manpower, Ammunition, Ration, and Part resources, which can be gathered in bulk indefinitely.
Storage
Android and iOS should be around 10GB.
Longetivity
This game will only ever end once they've told all the stories they want to tell. Which is still a lot as of now.

Is there PVP in this game?

There are two kinds of PVP in this game, the highscore leaderboards type (Theater and Event Ranking Maps) and direct (Luffberry Chess).

If you're looking for a more traditional PVP, luckily/unluckily this game doesn't have it.

How much daily engagement does this game need?

Minimal. Resources for pulls are generated passively. Events are months apart aka big bursts in-between lulls (in comparison to usual mobages).

How is the gacha in this game?

The only gacha in this game is cosmetics. Characters/Units/Dolls in this game do not go on a rotating banner, instead once they enter the "gacha pool", they're available permanently. In essence, this game is not a gacha game in terms of unit pulling.

Is it worth to reroll in this game?

Depends on what you value more. If you want a pretty easy time until endgame, game already gives you free strong dolls as part of the newbie missions. Endgame? This is a game of accumulating various tools instead of just a select few meta characters due to the volatile meta shifts. Collab units? They're not gacha or rather, you're guaranteed to get them with a working team.

TLDR; For the most part, the answer is no.

Is this game F2P?

Very much so to the point that quite a number of them are top rankers in major event rankings, the endgame. It's more about the breadth of units you have than the power of each individual unit, especially since you'll be using 20+ units per stage.

The only "P2W" is Protocol Assimilation, especially concerning Ringleaders, though it's more of pay to catch-up than anything. It's a major power boost to beginners, a crutch for mid-game players, and an occasional useful tool during end game.

How is the difficulty in this game?
Stage Gameplay Teambuilding Objectives Resources Priorities
Early game Simple auto-battle Any team is fine, using friend echelons advised Kill enemies, capture command posts Low resources and income, using MGs not recommended Building facilities and core units
Mid game Knowledge of class types and simple kiting Proper team formation required Objective completion varies Stable resource income Raising fairies (stat buffs) and HOCs (off-map supports)
Late game Advanced kiting, target resets, enemy attack delaying Specialized compositions focused on skill synergy Map gimmicks Abundant resources, mostly gets drained on production rate-up Raising specialist dolls (casually if preferred)
End game Ranking mald with kiting, crit i-frames As long as it works Map control and objectives Resources dwindling due to indiscriminate deployment Using duplicates is useful but not necessary

I heard they made new games of the same series. Is GFL1 going to be phased out?

Not anytime soon considering that they're still adding mechanics in its 7th year and there are more stories to tell. The plan is for all games to be played simultaneously.

Any guide thread I should read before starting out?
Gamepress
New Player Hub: How to Girls' Frontline
Archived version
GFL Corner
Website Guide
Spreadsheet Guide
Angry Trap Midget/Matsuda
Getting Started
First Steps
Guides
CosmicArcher
Walkthrough/Early Game Speedrun
Advanced Info
u/ConductorBichir
Reddit Pinned Posts
2.09 Starter Guide
June Tierlist (Isomer+) finalized by u/BichirMemoriam
Yuko #1428
Beginner's Guide to Girls' Frontline
u/ShuviSchwarze
Mashpit #1075
u/stae1234
Ceia
/gfg/
u/pointblanksniper
u/thaurelia

What should I focus on as a beginner?